The verdict in three sentences
For a Berlin Mittelstand company running a heavily customised SAP R/3 system ahead of an S/4HANA migration, RPA (software robots clicking through SAP GUI screens in place of operators) is the fastest path, but not the cheapest: 5 000 to 15 000 EUR per robot per year in licences, plus 3 000 to 8 000 EUR per scenario, and robots that break with every screen change. A custom API layer, wrapping RFC function modules and controlled database reads into REST services, costs 20 000 to 50 000 EUR from German integrators in 2026, yet often comes out at half the cost over 3 years once you automate more than 5 flows. RPA remains the right call if the S/4HANA cutover is within 18 months, or for one or two isolated flows.
Two approaches, two technical logics
RPA (UiPath, Power Automate Desktop, SAP Build Process Automation) replays a user's actions: open a transaction, enter an order number, copy a field. It requires no change to SAP, which appeals to IT teams dealing with custom Z-transactions that have no BAPI. The API layer instead exposes SAP data as web services that other tools (CRM, webshop, EDI, BI) call directly.
| Criterion (2026 estimate, German market) | RPA | Custom API layer |
|---|---|---|
| Licence | 5 000 to 15 000 EUR per robot per year | None (code delivered) |
| Development cost | 3 000 to 8 000 EUR per scenario | 20 000 to 50 000 EUR for the core |
| Lead time for a first flow | 2 to 4 weeks | 8 to 12 weeks |
| Processing speed | 1 to 3 minutes per transaction | Under one second |
| Sensitivity to screen updates | High, 15 to 25 % maintenance a year | Low, unless the data model changes |
| Real-time access for other tools | No, batch runs | Yes |
| Reusable after ERP change | No | Partly (API contract kept) |
The API layer relies on RFC access and standard BAPIs where they exist, and on read-only views of custom tables where they do not. Writes should go through BAPIs or IDocs so SAP business checks are never bypassed.
Total cost over 3 years for 10 automated flows
The comparison covers 10 flows: EDI orders, supplier invoices, material master creation, stock updates to the B2B shop, accounting export and five secondary flows. RPA needs 3 robots in production.
| 3-year item | RPA (market benchmark) | API layer, German integrator (market benchmark) | API layer, Kolonell grid |
|---|---|---|---|
| Licences | 72 000 EUR (3 robots at 8 000 EUR) | 0 | 0 |
| Initial development | 50 000 EUR (10 scenarios at 5 000 EUR) | 50 000 EUR (core 35 000 + flows 15 000) | 10 000 000 FCFA (15 240 EUR) |
| Maintenance and fixes | 30 000 EUR (20 % a year) | 15 750 EUR (15 % a year) | 6 480 EUR (Premium 120 000 FCFA/month) |
| Infrastructure | 6 000 EUR (virtual machines) | 4 500 EUR (hosting) | 4 500 EUR (hosting) |
| 3-year total | 158 000 EUR | 70 250 EUR | 26 220 EUR |
On Kolonell's grid, a complex application ranges from 7 000 000 to 15 000 000+ FCFA (10 670 to 22 870+ EUR); an API layer limited to 3 or 4 flows can stay in the mid band of 4 000 000 to 7 000 000 FCFA (6 100 to 10 670 EUR).
How to decide
| Your situation | Recommended choice | Reason |
|---|---|---|
| S/4HANA cutover signed within 18 months | RPA | Throwaway but fast |
| 1 or 2 flows, low volume (under 200 transactions a day) | RPA | API core not amortised |
| More than 5 flows or real-time need (B2B shop, EDI) | API layer | 3-year cost halved or better |
| No RFC or database access (locked hosting contract) | RPA | Only technical option |
| Migration 3 or more years away | API layer | The API contract survives the migration |
Mini case study
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Katrin, CIO of a 400-employee manufacturer in Berlin (illustrative example), needs to automate 10 flows on SAP R/3 before an S/4HANA migration planned for 2029. Today 3 operators spend about 60 % of their time re-keying data, 1.8 full-time equivalents at 55 000 EUR loaded, roughly 99 000 EUR a year. RPA at 158 000 EUR over 3 years saves 297 000 EUR, a net gain of 139 000 EUR. A German integrator's API layer at 70 250 EUR yields 226 750 EUR, and the same layer on Kolonell's grid at 26 220 EUR yields about 270 800 EUR, plus real-time stock access for the B2B shop. At migration, only the SAP-facing adapters are rewritten, so the webshop and EDI partners do not notice the cutover.
FAQ
Can we build an API on SAP R/3 without SAP Gateway?
Yes, through RFC calls from a middleware service, using standard BAPIs and custom function modules. Reads are simple; writes through BAPIs or IDocs account for 30 to 40 % of the core budget.
Why do RPA robots break?
A robot depends on field positions and labels on screen. A Windows update, a SAP GUI patch or a changed custom screen is enough to stop it, hence maintenance of 15 to 25 % of development cost per year.
Will the API layer work with S/4HANA?
The API contract (the services exposed to other tools) can be kept: only the part plugged into R/3 is rewritten, about 30 to 50 % of the initial cost. CRM, webshop and EDI do not see the migration.
How long until the first flow is live?
Expect 2 to 4 weeks with RPA and 8 to 12 weeks for an API layer, core included. Further flows on the API then ship in 1 to 2 weeks each.
Can we combine both approaches?
Yes, many mid-sized firms use RPA for 1 or 2 screens with no RFC access and the API for high-volume flows. It is often the cheapest setup when 80 % of flows go through the API.
Let's scope your project. Describe your SAP release, customisations and the list of flows to automate: we will price an API layer between 4 000 000 and 15 000 000 FCFA (6 100 to 22 870 EUR) depending on the number of flows, with a first flow live within 12 weeks. 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.
