What does a Checkout Extensibility migration actually cost for a mid-market Shopify Plus store with 5-10 custom checkout integrations?
No published figure exists. Here is the honest answer.
No published price exists for a Checkout Extensibility migration, because the work is priced per integration, not per store. Deploi's own decision record puts a full upgrade programme at $20,000 to $75,000 end to end over 8 to 14 weeks, with most landing in the $25,000 to $75,000 band (Deploi estimate, illustrative, September 2026). Integration count drives the number.
Why nobody publishes a figure
Shopify does not publish migration pricing and no agency rate card survives contact with a real checkout. Two Plus stores can both report "eight custom checkout integrations" and be a factor of four apart in cost, because the phrase covers everything from a shipping-rate rule with a published Function equivalent to a bespoke insurance-quoting widget with a partner API behind it.
So the useful answer is a breakdown by integration type, not a single number. Price each item, then add the programme overhead.
Cost by integration type
| Integration type | Replacement path | Relative cost | Notes |
|---|---|---|---|
| Discount or shipping rule with a like-for-like Function | Shopify Function, custom-built | Low to medium | The best case. Logic is portable, parity is testable |
| Discount logic with no one-to-one Function equivalent | Redesign the rule, then build | High | The rule itself gets renegotiated with merchandising. This is where schedules slip |
| Post-purchase upsell | App block on the new thank you page | Low, plus a subscription | Cost moves from build to recurring |
| Analytics and conversion tags | Web pixel or app pixel | Low to medium | Cheap to move, expensive to get wrong. See the sibling page on tracking tiers |
| Custom fields at checkout | Checkout UI extension | Medium | Layout is constrained by where blocks are allowed to sit |
| Third-party widget with a partner API | Vendor's own extension, if it exists | Unbounded | You are on the vendor's roadmap, not yours. Confirm existence before you scope |
| Branding and layout | Checkout Branding API | Low | Genuinely simpler than the checkout.liquid equivalent |
The programme numbers we use
Our checkout extensibility decision record scores the work BUILD and puts the end-to-end programme at $20,000 to $75,000, with most landing in the $25,000 to $75,000 range, over 8 to 14 weeks, plus roughly 15 to 20% of build cost annually in maintenance after cutover. The app-led alternative, where generic rules are bought rather than built, runs $500 to $3,000 in setup and $14,400 to $36,000 recurring over three years (Deploi estimates, illustrative, September 2026).
The Scripts-to-Functions piece is costed separately in its own record: $5,000 to $25,000 initial, roughly $7,250 to $40,000 over three years including maintenance, with 2 to 6 weeks to full cutover. The buy path there is $1,800 to $16,700 over three years (Deploi estimates, illustrative, September 2026).
A store with 5 to 10 integrations that are mostly the top two rows of the table sits in the lower half of the build band. A store with two or more of the "no equivalent" or "partner API" rows sits at the top of it, or above it.
What moves the number, ranked
- How many rules have no documented owner. Decompiling undocumented Script behavior takes longer than writing the Function that replaces it. Our decision record names this as the first build trap, and it is the single largest variance driver we see.
- Whether a parity harness gets built. Skipping it is cheaper on day one and produces silent drift that mirrors the silent failures you were migrating away from.
- App stacking. One Script inventory commonly needs two or three separate app subscriptions to replicate on the buy path. Budget the stack, not the app.
- Scope creep. Migrations attract checkout redesigns. Hold the parity map as the contract and phase the redesign separately, or the restoration becomes a rebuild.
When the honest answer is zero
An audit can come back clean. We have run audits that confirmed no exposure in days, and the correct verdict there is WAIT. Before commissioning anything, run the personalized report in Settings then Checkout, and the app audit in Settings then Apps, which Shopify generates for exactly this purpose (per Shopify Help Center, September 2026). That report is free and it is the cheapest scoping document available.
The Deploi point of view
Our own position, from building on Shopify. Separate from the facts above.
- Our take: Price this per integration and refuse to quote the store. Any fixed quote issued before the parity map exists is a quote for a scope neither party has seen, and it will be renegotiated in week four.
- What we’ve seen: The variance between two superficially identical Plus stores is almost entirely explained by how many checkout rules nobody can currently explain. That count, not the integration count, is the number worth asking for on the first call.
- Where we disagree: The category prices this as a technical migration with a per-integration rate. A meaningful share of the effort is a merchandising conversation about which rules should survive at all, and that time belongs in the estimate rather than hidden in contingency.
- What this page adds: the cost breakdown by integration type, the specific band from our two decision records, and the ranked list of variance drivers, with undocumented rule ownership at the top.
Reviewed by Martin Dejnicki, Director of SEO & AI Search. Facts verified 2026-09-14.