The verdict in three sentences
For a wholesaler asked by 15 key accounts to automate exchanges, a documented and secure partner REST API costs, as a 2026 order of magnitude, 30,000 to 80,000 GBP with a London agency, or 18,000 to 50,000 EUR with a French team, delivered in 8 to 12 weeks, plus 100 to 600 EUR a month for a managed API gateway. Against EDI billed 300 to 1,500 EUR per partner per month, the API becomes much cheaper from 4 or 5 connected partners. Security (OAuth2, rate limits, logging, versioning) is designed from the start, not after the first incident.
What a professional partner API includes
The CIO of a wholesaler (industrial supplies, food, electrical equipment) receives orders by email, PDF or web portal, then rekeys them into the ERP. Customers now ask for real-time stock availability and shipment tracking. The API exposes this data in a controlled way.
| Component | Scope | Indicative budget (French team) | Timeline |
|---|---|---|---|
| API design and contract | Resources, OpenAPI 3.1 schemas, error conventions | 2,000 - 5,000 EUR | 1 - 2 weeks |
| Business endpoints | Catalog, customer net prices, stock, orders, shipments, invoices | 7,000 - 20,000 EUR | 3 - 5 weeks |
| ERP connector | Read and write to the ERP (Sage, SAP B1, Microsoft Dynamics, NetSuite) | 3,000 - 10,000 EUR | 2 - 3 weeks |
| Security | OAuth2 client credentials, per-partner scopes, encryption, rate limits | 2,500 - 6,000 EUR | 1 - 2 weeks |
| Developer portal | Interactive docs, sandbox, test keys | 1,500 - 5,000 EUR | 1 - 2 weeks |
| Testing and go-live | Load tests, logging, alerts, acceptance with 2 pilot partners | 2,000 - 4,000 EUR | 1 - 2 weeks |
| Total | 18,000 - 50,000 EUR (30,000 - 80,000 GBP in London) | 8 - 12 weeks |
A managed API gateway (Azure API Management, AWS API Gateway, Kong, Gravitee) costs 100 to 600 EUR a month depending on call volume and features (caching, analytics, portal). Annual maintenance is 12 to 15% of the build budget. London day rates for senior API engineers run around 600 to 900 GBP, which explains the higher range.
API vs EDI: the 5-year comparison
EDI (EDIFACT or ANSI X12 through a value-added network provider) remains the norm with large retailers. But its recurring per-partner cost weighs heavily on a mid-sized wholesaler.
| Criterion (15 partners, 5 years) | EDI via provider | Custom REST API |
|---|---|---|
| Setup | 1,000 - 3,000 EUR per partner, so 15,000 - 45,000 EUR | 35,000 EUR (one-off) |
| Recurring cost | 300 - 1,500 EUR per partner per month | 300 EUR a month of gateway |
| Recurring cost over 5 years | 270,000 - 1,350,000 EUR | 18,000 EUR |
| Maintenance | Included with the provider | 5,250 EUR a year, so 21,000 EUR over 4 years |
| Onboarding a new partner | 1,000 - 3,000 EUR and 2 - 6 weeks | 500 - 1,500 EUR and 1 - 2 weeks |
| Real-time data (stock) | No, batch exchanges | Yes |
| 5-year total (low EDI assumption) | 285,000 EUR | 96,500 EUR (including 22,500 EUR of onboarding) |
A hybrid approach is common: EDI for the 2 or 3 retailers that require it by contract, the API for everyone else.
Security: the 2026 minimum requirements
An API exposing net prices, stock and orders becomes a target. Minimum requirements follow the OWASP API Security Top 10: OAuth2 authentication with short-lived tokens (15 to 60 minutes), per-partner scopes so one customer never sees another's prices, rate limits (for example 600 requests per minute per partner) so a faulty script cannot saturate the ERP, timestamped logging kept for 12 months, and TLS 1.3 encryption. Add explicit versioning (/v1, /v2) with 12 months' notice before any removal, and load tests simulating 5 times the expected peak. A targeted penetration test costs 4,000 to 8,000 EUR and reassures key accounts' security teams during supplier onboarding.
Mini case study
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Priya, CIO of a 120-person industrial supplies wholesaler near London, receives 1,200 orders a month from 15 key accounts, each rekeyed in 8 minutes: 160 hours a month, or 61,440 GBP a year at a loaded cost of 32 GBP an hour. With a 1.5% keying error rate at an average cost of 130 GBP each (returns, credit notes, freight), she also loses 28,080 GBP a year, 80% of which disappears with the API: 22,464 GBP. Total gain: 83,904 GBP a year. For an API at 55,000 GBP and 8,000 GBP of yearly running costs (gateway and maintenance), payback comes in about 8.7 months.
FAQ
How much does ERP API development cost in 2026?
As an order of magnitude, 30,000 to 80,000 GBP in London or 18,000 to 50,000 EUR with a French team, for a documented and secure REST API in 8 to 12 weeks. A scope limited to stock and orders starts around 12,000 EUR.
Does the API fully replace EDI?
Not always: some retailers require EDI by contract. The API covers other partners and removes recurring fees of 300 to 1,500 EUR per partner per month.
How do we stop a partner from overloading our ERP?
With per-partner rate limits (for example 600 requests per minute), caching on catalog data and a queue for write operations. These protections add 1,500 to 3,000 EUR.
How long does it take to onboard a new partner?
With OpenAPI documentation and a sandbox, 1 to 2 weeks on the partner side, and 500 to 1,500 EUR of support on the wholesaler side.
How do we evolve the API without breaking integrations?
Through explicit versioning (/v1, /v2), backward-compatible changes by default and 12 months' notice before retiring a version.
Let's scope your project. We define your partner API (endpoints, security, ERP connector, pilot onboarding) within an 18,000 to 50,000 EUR budget and an 8 to 12 week timeline. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
