The verdict in three sentences
If an existing vertical SaaS covers more than 80 % of your need, buy it: you go live in weeks at a predictable cost. If your process is differentiating — it is what wins you clients — or if you exceed 25 to 40 users, custom becomes rational because per-seat SaaS eventually overtakes the amortised cost of a proprietary asset. In between, decide on real functional coverage, not on the sales demo.
The two cost models in 2026
SaaS charges a recurring subscription that scales with headcount. Custom demands a high upfront investment, then annual maintenance (ATMP) of 18 to 22 % of the build. The 2026 order of magnitude on the London market:
| Item | Vertical SaaS | Custom build |
|---|---|---|
| Upfront cost | 0 to 5,000 EUR (setup) | 45,000 to 110,000 EUR |
| Recurring cost | 25 to 80 EUR / user / month | Maintenance 18 to 22 % of build / year |
| Time to production | 2 to 8 weeks | 4 to 9 months |
| Business fit | 60 to 90 % (standard) | 95 to 100 % (targeted) |
| Code ownership | No (licence) | Yes (asset) |
| Vendor lock-in | High | None to low |
The classic trap: comparing only the entry price. Over 4 years, SaaS at 50 EUR per seat for 30 users is 72,000 EUR before price hikes — already in the range of a build.
The five-criteria decision grid
| Criterion | Leans buy (SaaS) | Leans build (custom) |
|---|---|---|
| Standard functional coverage | > 80 % | < 70 % |
| Number of users | < 25 | > 40 |
| Differentiating nature of process | Low | Strong (competitive edge) |
| Need for specific integrations | Few | Many / proprietary |
| Amortisation horizon | < 2 years | 3 to 5 years |
Simple rule: add up the rows. Three or more criteria on the right justify a build study; otherwise, a well-chosen SaaS saves you time and cash.
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Mini case study
Remi runs a 34-person logistics SME in London. The route-planning SaaS he is evaluating costs 62 EUR per user per month for 30 seats, i.e. 22,320 EUR per year, with an announced 7 % annual rise. Over 5 years that is about 128,000 EUR. The custom quote comes in at 78,000 EUR for the build plus 20 % maintenance (15,600 EUR/year), i.e. 156,000 EUR over 5 years — but with a proprietary route-optimisation module that, by his figures, saves 6 % of fuel, roughly 19,000 EUR per year. Break-even under 4 years, and the asset stays on the balance sheet: Remi commits to the build.
FAQ
Is custom always more expensive upfront? Yes, almost always: budget 45,000 to 110,000 EUR versus a subscription starting at a few hundred euros a month. The gap reverses with user volume and length of use.
What is the real SaaS risk? Vendor lock-in and price drift: 5 to 10 % annual increases, add-ons billed separately, and sometimes limited data export. Provision a reversibility clause from the contract onward.
Above how many users does building make sense? The 2026 order of magnitude is 25 to 40 users for intensive use, but the decisive criterion remains how differentiating the process is, not headcount alone.
Can you start on SaaS then switch to custom? Yes, it is a prudent path: validate the need on SaaS for 12 to 18 months, then build once processes stabilise. Demand a full data export to prepare migration.
How much does maintaining custom software cost? Budget annual maintenance of 18 to 22 % of the build cost, covering fixes, evolutions and security. It is the line leaders most underestimate.
Let's scope your project. Tell us your headcount, your differentiating processes and an indicative budget, and we produce a 5-year build vs buy grid. 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.
