A mid-market BigCommerce build runs between $25,000 and $80,000 according to BigCommerce's own published ranges, and an enterprise build can cross $250,000 once headless and integrations are layered in. The spread between a $30,000 proposal and a $130,000 proposal for work that looks similar on a sales deck is almost entirely about who wrote the proposal. This guide exists because the wrong agency decision costs more than a good one. A retailer who picks a generic ecommerce shop over a platform-specific agency typically discovers the gap three months after launch, when the Stencil theme cannot accommodate the feature the business needs, the checkout extension breaks under the Checkout SDK's CORS constraint, or the ERP integration turns out to be a nightly CSV job instead of real webhook sync.
The parent guide covers the broader BigCommerce development topic. This page stays narrow. It covers agency evaluation, cost benchmarks in 2026 dollars, and the specific questions that separate agencies that know the platform from agencies that are learning on your invoice.
Why BigCommerce experience is not interchangeable with generic ecommerce experience
Three platform-specific realities change what agency skill actually means on BigCommerce. Stencil themes compile through a CLI-driven local workflow with Handlebars and SCSS, not through an online editor. The Checkout SDK cannot call the BigCommerce storefront checkout from outside the storefront host because the storefront web APIs do not currently support CORS, which means a headless site that wants to keep the native Optimized One-Page Checkout usually embeds it via the SDK's embedded-checkout module rather than rebuilding the flow from scratch. Catalyst, the reference headless stack, moved its main branch to frozen in January 2025 and now ships from the canary branch running Next.js 16, React 19, and Node.js 24 or higher, which bumps into infrastructure choices that teams used to Stencil's Node 20 and 22 support may not have planned.
None of those facts appear in a generalist ecommerce agency's pitch deck. The agency that has not hit the CORS wall, has not managed a Node 24 CI pipeline, and has not shipped a Catalyst upgrade into production will learn those lessons on your project. The learning is not free. Budget overruns on first-time BigCommerce builds tend to land between 20 and 45 percent according to aggregated partner feedback, almost always tied to a feature the agency assumed was trivial and turned out to be a platform constraint.
Agencies that offer dedicated BigCommerce development services typically scope B2B projects differently than general ecommerce shops because the platform's B2B Edition requires specialized configuration for company accounts, quote management, and purchase order workflows. The difference shows up in the discovery call. A specialist asks about account hierarchy depth, whether sales rep masquerade is needed, and how the quote-to-order conversion should route into the ERP. A generalist asks about "B2B features" and proposes a native customer group build that will need to be replaced eighteen months later.
The agency question is not whether they have done ecommerce. The agency question is whether they have shipped the exact BigCommerce feature you need, inside the last twelve months, into a store generating real revenue.
The eight-criteria evaluation framework
Every agency pitch looks reasonable on a website. The differences surface when a buyer measures them against a consistent framework. Use all eight criteria, and weight them against the project type. A theme customization project cares less about API and integration depth. A B2B build cares a lot about it.
1. BigCommerce partner tier and certification
The BigCommerce partner program publishes tiers including Elite, Preferred, and Certified, and the partners directory filters by those tiers. Elite status signals revenue volume and certified staff count, not necessarily the best technical fit, but it correlates with longevity and account team access. A good screening rule is to prefer Preferred or Elite Partners for enterprise work and to accept Certified Partners for SMB work if the technical interview goes well.
2. Platform-specific portfolio, scoped to the last 12 months
Agency portfolios often include stores built five or six years ago on architectures that have since changed. The technical debt of a 2019 Stencil theme and a 2025 Catalyst storefront is not comparable. Ask for three live stores shipped in the trailing 12 months, in your industry or an adjacent one, and then actually run Lighthouse on them.
3. Integration depth with a stated architecture
ERP, CRM, PIM, and marketing stack integrations are the work that determines whether the build ships on time. Ask the agency to sketch the integration architecture on a whiteboard or a Miro board live. A specialist will draw webhooks, iPaaS middleware, and fallback reconciliation jobs. A generalist will draw a single arrow between two boxes.
4. Stencil and Catalyst fluency with version specifics
"Yes we know Stencil" is not the same as "we have shipped a Catalyst app this year and we know the canary branch upgrade path from Next 15 to Next 16." Ask which version of the Stencil CLI the team uses day to day, whether they build Catalyst projects locally on Node 24, and how they handle upgrades when BigCommerce ships breaking changes to the GraphQL Storefront API schema.
5. Quality assurance and accessibility discipline
Ask for their QA checklist. Agencies with mature practices have a written document covering WCAG 2.2 AA, Core Web Vitals thresholds, cross-browser matrix, mobile device matrix, accessibility smoke tests with a screen reader, and a launch-day rollback procedure. Agencies without one will say they "test thoroughly" and mean it.
6. Discovery process and scope rigor
A good discovery produces a written technical design document, an integration map, a redirect inventory if applicable, and a cutover runbook. It also produces a list of platform constraints the agency identified for your project. If the discovery deliverable is a one-page statement of work, the agency is either charging too little for discovery or moving too fast to find the problems. Either failure mode costs more later.
7. Post-launch support and SLA clarity
The launch is the start. What happens 30, 60, and 180 days after launch is where support quality shows. Look for a named account manager, a documented escalation path, a response-time SLA during business hours, and an on-call option for checkout and payment incidents. Retainers in the 2026 market run from about $500 per month for light maintenance on a small Stencil store to $5,000 or more per month for a B2B store with active integration work.
8. Pricing transparency and no-surprise contracts
Look at the rate card, the change-order procedure, and what counts as billable versus included. A typical pattern is an agency quoting low on the initial build and recovering margin on change orders after the scope expands during development. Ask what happens if the scope does not expand. A confident agency answers the question directly.
Agency, freelancer, or staff augmentation
Three engagement models dominate BigCommerce work in 2026 and they differ on more than price. Freelancers typically charge between $25 and $100 per hour depending on region and seniority, and they work well for theme customization, small app builds, bug-fix retainers, and short-cycle enhancements. The freelancer risk is single-person dependency. If the freelancer takes a long vacation or changes clients, the project stalls.
Agencies typically charge between $100 and $300 per hour, bundle multiple disciplines under one project manager, and work well for full builds, replatforms, headless projects, and anything that touches more than two systems. The agency risk is overhead. A six-person team on a four-person project burns through the budget on coordination rather than code.
Staff augmentation sits in the middle. A BigCommerce-focused staffing firm places one or two engineers inside your team on a monthly retainer, typically $8,000 to $18,000 per engineer per month depending on seniority and region. It works well when the in-house team needs capacity more than it needs leadership. The risk is institutional knowledge drift. Engineers who rotate off the project at the end of the contract take what they learned with them unless documentation is a contractual deliverable.
2026 cost benchmarks by project type
The numbers below reflect aggregated 2026 project data, with specific anchor points from BigCommerce's own published cost articles and partner benchmarks. Ranges assume a US-based agency at the mid to upper end and a nearshore or partially offshored team at the lower end. Pure-offshore builds can come in 25 to 40 percent lower, with the coordination overhead and quality variance that implies.
| Project type | Cost range | Typical timeline | Team shape |
|---|---|---|---|
| Theme customization on Cornerstone or marketplace theme | $2,000 to $8,000 | 2 to 5 weeks | 1 developer, 1 designer part-time |
| Custom BigCommerce app or internal tool | $5,000 to $25,000 | 4 to 10 weeks | 1 to 2 developers |
| Full DTC build on Stencil | $15,000 to $60,000 | 6 to 16 weeks | 2 developers, 1 designer, 1 PM |
| Full DTC build on Catalyst (headless) | $45,000 to $150,000 | 12 to 24 weeks | 2 to 4 developers, 1 designer, 1 PM, 1 DevOps |
| B2B build with B2B Edition plus ERP integration | $25,000 to $80,000 base, plus integration | 12 to 28 weeks | 2 to 4 developers, 1 integration specialist, 1 PM |
| Enterprise headless with multi-storefront plus integrations | $150,000 to $400,000 or higher | 20 to 40 weeks | Cross-functional squad of 6 to 10 |
| Ongoing maintenance retainer | $500 to $5,000 per month | Indefinite | Fractional engineer plus shared support |
A few numbers on the platform itself matter for budgeting. BigCommerce Standard lists at $39 per month, Plus at $105 per month, and Pro at $399 per month as of 2026, with Enterprise quoted individually. Transaction fees are zero through the payment processor configured on the store, which is unusual versus Shopify's processor surcharge on non-Shopify Payments. US agency hourly rates cluster around an average of roughly $52 per hour with an interquartile range of approximately $40 to $65 per hour, though platform specialists with Catalyst or B2B Edition experience can quote above $150 per hour and justify it.
Cost questions continue in the dedicated BigCommerce customization cost breakdown and the architectural decision that often drives the biggest cost delta is covered in Stencil versus headless BigCommerce.
Red flags that appear in the proposal
Bad-faith or simply mismatched agencies leak signals into the sales cycle. Any one of these is a yellow flag. Two or more in the same proposal is a reason to pass.
The proposal uses the word "custom" without naming the actual deliverable. Custom what. Custom theme work is cheap. Custom checkout code is not. If the proposal cannot tell you which Stencil template files are being touched or which API endpoints are being called, the agency has not finished discovery.
The proposal is suspiciously fast or suspiciously cheap compared to two other quotes. Fast and cheap usually means the agency plans to reuse a prior build's code wholesale, which works fine until it does not, at which point the maintenance invoice climbs. Ask how much of the work is new code versus reused. Expect an honest answer.
Outsourcing is not disclosed. An agency that subcontracts part of the work to a team in another country is not inherently a problem. An agency that hides that fact is. Ask directly during discovery. Ask who the named engineers will be. Ask whether they work for the agency full time or contract.
Post-launch support is vague or priced as a separate future conversation. A good agency has a defined support tier structure and proposes the tier alongside the build. A weaker agency treats support as a cross-sell. By the time the cross-sell conversation happens, the in-house team is already suffering.
Change-order rates are not disclosed. A fair agency publishes its change-order hourly rate in the master services agreement, typically at a 10 to 25 percent premium over the blended build rate. An agency that cannot quote that number is planning to negotiate it in the moment, which favors the agency and not the buyer.
Contract clauses that matter on a BigCommerce project
Standard agency master services agreements often miss four clauses that matter specifically on BigCommerce work. A buyer who asks for them before signing gets most of them without pushback. A buyer who asks after launch rarely gets any.
The first is repo ownership. Stencil themes and Catalyst projects live in Git repositories the agency typically owns during the build. The contract should state that on final payment, ownership of the repository transfers to the client, with full commit history and any private submodules. This one sentence prevents the worst lock-in outcome, which is a client who owns the live store but cannot access the source that generated it.
The second is API credential handling. The agency needs BigCommerce API credentials, payment gateway credentials, and often ERP and CRM credentials to do the work. The contract should specify that credentials are stored in a password manager that transfers to the client, that credentials are rotated at project handoff, and that the agency logs which environments touched production data during QA.
The third is acceptance testing with defined pass criteria. Agencies ship at different quality bars. A contract that names specific pass criteria turns a subjective "done" into a checklist. Typical items include Lighthouse performance above 85 on mobile, Core Web Vitals all green, WCAG 2.2 AA pass, checkout success rate above 95 percent in a 20-order smoke test, and webhook delivery reliability above 99 percent over a 48-hour burn-in.
The fourth is warranty window with defined response times. Most agencies offer a 30 or 60 day warranty for bugs introduced during the build. A contract should specify response times during the warranty window, what counts as a warranty fix versus a change request, and whether P1 incidents get on-call coverage during the first two weeks after launch.
Eight questions to ask before signing
Ask all eight during the second discovery call, after the initial pitch and before the statement of work lands in the inbox. The goal is not a gotcha. The goal is to force specifics out of the sales cycle, where specifics survive, and into the contract, where specifics matter.
- Which three BigCommerce stores did you ship in the last 12 months, in our industry or an adjacent one, and can we contact one client for reference?
- What Stencil CLI version and what Catalyst branch are your developers using this week on their most recent project?
- Walk us through the integration architecture live. Where do webhooks land. What is the fallback when a webhook fails. What iPaaS or middleware do you default to and why.
- What is your written QA checklist for launch and can we see a redacted copy from a recent project.
- Who is the named project manager, who are the named engineers, are any of them contractors or subcontracted to another firm, and what is their tenure with your agency.
- What is the change-order hourly rate and how do you decide when a scope clarification is a change order versus an included refinement.
- What post-launch support tiers do you offer, what response times apply to P1, P2, and P3 incidents in each tier, and can we start the retainer one week before launch rather than after.
- On final payment, what transfers to us: source code repositories, commit history, API credentials in a password manager, infrastructure access, design files in editable format, and content in a portable export.
Case study
A Dallas-based industrial distributor with $12 million in annual revenue ran a selection process in late 2025 for a B2B Edition rebuild with a NetSuite integration. Three agencies bid. The low bid was $38,000 from a generalist ecommerce shop with no published BigCommerce portfolio. The middle bid was $72,000 from a BigCommerce Preferred Partner with two B2B Edition references. The high bid was $118,000 from an Elite Partner with a Catalyst reference and a named NetSuite integration lead.
The distributor picked the middle bid. The build took 16 weeks against a planned 12. Overrun was driven by a customer group pricing reconciliation against NetSuite item price levels, which required 40 additional engineering hours that neither party had forecast. Final invoice landed at $81,000, roughly 12 percent over the original quote. Post-launch the retainer runs at $3,200 per month covering webhook reliability, integration drift, and quarterly Stencil theme updates.
The lesson was not that the middle bid was right. The lesson was that the discovery conversation missed the customer group to NetSuite price level mapping, which surfaced in week six and cost both parties time. A discovery deliverable that included a field-by-field integration map would have caught the gap before the statement of work was signed.
Frequently asked questions
- How much does a BigCommerce development agency cost in 2026?
- Typical US agency rates sit between $100 and $300 per hour, with specialists on Catalyst or B2B Edition at the upper end. Full DTC builds on Stencil run $15,000 to $60,000. Full builds on Catalyst run $45,000 to $150,000. B2B builds start around $25,000 and commonly exceed $80,000 once ERP integration is included. Ongoing maintenance retainers run $500 to $5,000 per month depending on store complexity.
- What certifications should a BigCommerce development agency have?
- Look for current BigCommerce Partner status with a tier of Certified, Preferred, or Elite shown in the official partner directory. For B2B work, look for explicit B2B Edition references with live store examples. For headless work, look for shipped Catalyst or custom headless builds rather than demo stores. Certifications are a screen, not a proof. Verify with case studies and client references.
- What is the difference between a BigCommerce freelancer and an agency?
- Freelancers run $25 to $100 per hour, work well on single-skill tasks like theme work or small apps, and carry single-person delivery risk. Agencies run $100 to $300 per hour, bundle designer, developer, QA, and PM under one contract, and work better for full builds, replatforms, and any project touching more than two systems. Staff augmentation, at $8,000 to $18,000 per engineer per month, sits between the two and works when an internal lead exists and capacity is the bottleneck.
- How long does a BigCommerce build take?
- Theme customization runs 2 to 5 weeks. A full DTC build on Stencil runs 6 to 16 weeks. A Catalyst headless build runs 12 to 24 weeks. A B2B build with B2B Edition plus ERP integration runs 12 to 28 weeks. Enterprise multi-storefront builds run 20 to 40 weeks or longer. Scope changes are the single biggest driver of overrun across every project type.
- What happens if a BigCommerce agency goes out of business during the project?
- The risk is real enough to contract around. Require source code to be pushed to a client-owned Git repository weekly rather than only at milestones. Require production credentials to live in a password manager under dual control. Require written acceptance criteria on each milestone so partial work can be handed to another agency if needed. A well-structured contract reduces a full project loss to a few weeks of transition time and a short-notice search for a replacement team.