The verdict in three sentences
In 2026, a London accounting firm chooses between a vertical SaaS at 30-90 EUR per user per month and a custom build at 45,000-120,000 EUR amortised over three years. SaaS wins below 8 staff; custom becomes profitable past 15 users and especially when you want a GED client portal integrated with your production accounting software. The real variable is not the sticker price but the 3-year total cost of ownership, including integration and GDPR.
Vertical SaaS or custom build: 2026 prices
The London market offers three routes. A vertical SaaS bills per active user. Custom gives you code ownership and tight integration with your production chain. The hybrid starts from an open-source base you customise.
| 2026 option | Entry cost | Recurring cost | Ownership |
|---|---|---|---|
| Standard vertical SaaS | 0-2,000 EUR setup | 30-90 EUR/user/mo | No |
| SaaS + premium modules | 3,000-8,000 EUR | 60-120 EUR/user/mo | No |
| Full custom build | 45,000-120,000 EUR | 800-2,200 EUR/mo maintenance | Yes |
| Open-source hybrid | 25,000-55,000 EUR | 500-1,500 EUR/mo | Yes (code) |
| GED client portal (option) | +8,000-20,000 EUR | included in maintenance | Depends on base |
Allow 3 to 6 months for a custom build with data migration and a connector to your production software. A SaaS deploys in 3 to 6 weeks but imposes its functional limits.
3-year TCO: the real trade-off
The monthly SaaS price looks low, but it multiplies by the number of users and by 36 months. Here is a 2026 order of magnitude for a 12-staff firm.
| 3-year item | SaaS 70 EUR/user | Custom |
|---|---|---|
| Licences / initial build | 0 EUR | 85,000 EUR |
| Subscriptions 12 users x 36 mo | 30,240 EUR | 0 EUR |
| Maintenance / hosting | included | 43,200 EUR |
| Production accounting integration | 6,000 EUR | included |
| GED client portal | +25,200 EUR (option) | +14,000 EUR |
| 3-year total | 61,440 EUR | 142,200 EUR |
At 12 users SaaS stays cheaper, but without ownership or a custom portal. Add 8 staff or a deep integration need and custom becomes strategically superior over 5 years.
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Mini case study
Marc, partner of a 14-staff accounting firm in central London, paid 68 EUR/user/month, i.e. 11,424 EUR/year for SaaS, plus 4 weekly hours lost re-keying between the management tool and the production software. We delivered a custom base at 78,000 EUR with a native connector and a GED client portal. Gain: 208 hours/year recovered (52 weeks x 4 h), valued at 60 EUR/loaded hour, i.e. 12,480 EUR/year. Amortised in just under 5 years versus SaaS, but profitable from year 2 once regained billable time is counted.
FAQ
How much does a custom build really cost in 2026? Expect 45,000 to 120,000 EUR depending on modules (engagement management, time, billing, client portal). A mid-sized firm sits around 75,000-90,000 EUR.
Is SaaS cheaper than custom? Below 8 users, almost always. Between 12 and 15 users the 3-year gap drops below 80,000 EUR and custom wins on usage value and ownership.
How much is the GED client portal? Roughly 8,000 to 20,000 EUR of additional development, or 25,000 EUR over 3 years as a SaaS option for 12 users. It cuts collection emails by 40 to 60 %.
What are the rollout timelines? 3 to 6 weeks for a SaaS, 3 to 6 months for a custom build including data migration and a production accounting connector.
Does GDPR change the budget? Yes, plan for EU hosting, access logging and a retention policy: 3,000 to 8,000 EUR of compliance built in by design.
Let's scope your project. Tell us your headcount, your current production software and your client-portal need: we price SaaS vs custom over 3 years with a clear indicative budget. 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.
