The verdict in three sentences
Moving from 3 on-premise clients to a multi-tenant SaaS costs between 120,000 and 400,000 USD with a New York agency, and hosting rises from almost nothing to 300 to 3,000 USD a month. The structuring choice is the data isolation model: shared database with row-level isolation, schema per tenant or dedicated database, each with a very different running cost at 50 then 500 clients. At Kolonell, this kind of rebuild is a complex application, between 7,000,000 and 15,000,000+ FCFA (10,670 to 22,870+ EUR, about 12,000 to 26,000+ USD), depending on how much existing code can be reused.
Three isolation models, three cost profiles
A New York software vendor selling business software installed on-premise (or on one dedicated server per client) currently manages three versions, three databases and three update procedures. Moving to SaaS means a single codebase, a single deployment and client onboarding in minutes. The isolation model drives security, ease of migrations and the hosting bill.
| Criterion | Shared database, row-level isolation | Schema per tenant | Dedicated database per tenant |
|---|---|---|---|
| Principle | tenant_id column + PostgreSQL RLS policies | One PostgreSQL schema per client | One database instance per client |
| Build cost | Lowest (baseline) | +10 to 20% | +20 to 35% |
| Hosting at 50 clients | 300 to 600 USD/month | 500 to 900 USD/month | 1,200 to 3,000 USD/month |
| Schema migrations | One | One per schema, scripted | One per database, orchestrated |
| Cross-tenant leak risk | Controlled if RLS is tested | Low | Very low |
| Enterprise sales argument | Medium | Good | Excellent (isolated data, simple export) |
| Recommended for | 20 to 2,000 SMB clients | 10 to 300 mid-market clients | Fewer than 50 demanding clients (health, finance) |
For most B2B vendors, the shared database with Row Level Security is the best compromise, provided you write automated tests proving a tenant can never read another's data. The hybrid model (shared database by default, dedicated database sold as an Enterprise option) is becoming the norm in 2026.
The budget line by line
| Item | Share of budget | New York agency range |
|---|---|---|
| Multi-tenant layer (tenants, roles, RLS, subdomains) | 15 to 20% | 25,000 to 70,000 USD |
| Reuse and refactoring of existing business code | 30 to 40% | 40,000 to 150,000 USD |
| Subscription billing (Stripe Billing, plans, limits) | 8 to 12% | 10,000 to 45,000 USD |
| Self-service onboarding and data import | 8 to 12% | 10,000 to 45,000 USD |
| Infrastructure, CI/CD, backups, monitoring | 10 to 15% | 15,000 to 55,000 USD |
| Migration of the 3 on-premise clients | 5 to 10% | 8,000 to 35,000 USD |
| Security, SOC 2 readiness and penetration tests | 5 to 8% | 8,000 to 30,000 USD |
Reusing existing code is the most uncertain item. Recent, tested, modular code can be 60% reused. Ten-year-old code written for a single install often requires rewriting the business core. A 5 to 8 day audit before pricing avoids bad surprises.
Mini case study
Illustrative example: Julien, founder of a construction management software vendor in New York, serves 3 on-premise clients who each pay a 20,000 USD licence plus 4,000 USD of annual maintenance. He targets 60 SaaS clients at 500 USD a month within 3 years.
- Rebuild cost: 250,000 USD with a New York agency, or 12,000,000 FCFA (about 18,290 EUR, roughly 21,000 USD) with Kolonell.
- Shared-database hosting at 60 clients: about 500 USD a month, i.e. 6,000 USD a year.
- Target recurring revenue: 60 x 500 x 12 = 360,000 USD a year.
- Break-even: about 42 clients over one year with the local agency, about 5 clients with Kolonell, hosting and Premium maintenance (120,000 FCFA a month) included.
The main lever remains sales: the SaaS only creates value if the team sells 1 to 2 new subscriptions a month.
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FAQ
How much does moving from on-premise software to multi-tenant SaaS cost?
Between 120,000 and 400,000 USD with a New York agency depending on code reuse. At Kolonell, expect 7,000,000 to 15,000,000+ FCFA, i.e. 10,670 to 22,870+ EUR.
Which isolation model should we choose?
A shared database with Row Level Security suits 20 to 2,000 SMB clients. A dedicated database makes sense for fewer than 50 demanding clients in health or finance, with hosting 3 to 5 times more expensive.
How much does B2B SaaS hosting cost?
From 300 to 600 USD a month for 50 clients on a shared database, up to 3,000 USD a month with dedicated databases. Choosing a US region on AWS, GCP or Azure keeps latency low for American clients.
What about clients already installed on-premise?
Migrate them last, one at a time, with a data import tested on a copy. Plan 8,000 to 35,000 USD and a 2 to 4 week parallel run.
How long does the rebuild take?
From 4 to 9 months depending on code quality. Launching with a pilot client in month 4 validates billing and onboarding before the commercial opening.
Let's scope your project. Share your current stack and your 3-year client target: we will price the multi-tenant rebuild between 7,000,000 and 15,000,000 FCFA with a 4 to 9 month migration plan. 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.
