The verdict in three sentences
A vendor maintaining one installation per client ends up spending more time deploying releases than building its product. Moving to a multi-tenant B2B SaaS costs EUR 60,000 to 150,000 excl. VAT in 2026 for a mid-sized vendor in Montreal (roughly CAD 90,000 to 225,000), and cuts cloud cost per client by 3 to 5. The structural choice is between a shared database with tenant isolation and a database per client, with SAML SSO as an almost systematic enterprise requirement.
The starting point: one installation per client
The pattern is common among B2B vendors born in the 2000s and 2010s: each client has its own server or virtual machine, its own database and sometimes its own version of the code. With 80 clients, that means 80 environments to monitor.
The symptoms:
- A release takes 2 to 4 weeks to roll out to all clients, and some remain stuck on old versions.
- Infrastructure cost per client is EUR 150 to 400 excl. VAT a month, even for a small account.
- Support has to reproduce bugs on each client's exact version.
- Onboarding a new client takes 2 to 5 days of technical work.
| Criterion | One installation per client | Multi-tenant SaaS |
|---|---|---|
| Cloud cost per client | EUR 150 to 400 excl. VAT a month | EUR 30 to 100 excl. VAT a month |
| Release deployment | 2 to 4 weeks | A few minutes, continuous |
| Versions in production | 5 to 15 in parallel | Just 1 |
| Client onboarding | 2 to 5 days | A few minutes, self-service possible |
| Monitoring | 80 environments | 1 platform |
| Per-client customisation | Code forks | Settings and toggleable modules |
Shared database or database per client
This is the decision that drives budget, security and running costs.
| Model | Principle | Advantages | Limits | Relative cost |
|---|---|---|---|---|
| Shared database, tenant column | All data in the same tables, filtered by ID | Lowest cost, simple deployment | Logical isolation only, requires strict discipline | 1 |
| Shared database + row level security | Same principle, isolation enforced by the database (PostgreSQL RLS) | Good security and cost balance | Queries harder to optimise | 1.2 |
| Schema per client | One database, one schema per tenant | Stronger isolation, easy export | Migrations applied to N schemas | 1.5 |
| Database per client | One dedicated database per tenant | Maximum isolation, data residency possible | Cost and migrations multiplied | 2 to 3 |
| Hybrid | Shared for SMEs, dedicated for enterprise | Sellable premium offer | Two modes to maintain | 1.5 to 2 |
For a vendor selling to both SMEs and a few enterprise accounts, the hybrid model is often the most profitable: the shared database with RLS serves 90% of clients, and the dedicated database is billed as an option.
The rebuild budget in 2026
| Workstream | Content | 2026 budget excl. VAT (Montreal) |
|---|---|---|
| Scoping and architecture | Model choice, breakdown, migration plan | EUR 6,000 to 12,000 |
| Multi-tenant layer | Isolation, tenant management, settings | EUR 15,000 to 35,000 |
| Authentication | Accounts, roles, SAML SSO and OpenID Connect | EUR 8,000 to 18,000 |
| Billing and subscriptions | Plans, quotas, Stripe or equivalent integration | EUR 6,000 to 15,000 |
| Infrastructure and CI/CD | Containers, continuous deployment, monitoring | EUR 10,000 to 25,000 |
| Migration of existing clients | Moving N databases to the target model | EUR 10,000 to 30,000 |
| Security and compliance | Penetration tests, logging, privacy law (Quebec Law 25, GDPR) | EUR 5,000 to 15,000 |
The total falls between EUR 60,000 and 150,000 excl. VAT, over 6 to 12 months. SAML SSO deserves special attention: enterprise IT departments ask for it in 70 to 90% of tenders, and it often gates access to contracts worth more than EUR 50,000 a year.
Mini case study
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Marc, CTO of an industrial planning software vendor in Montreal (illustrative persona), serves 80 clients each installed on their own virtual machine.
- Current infrastructure cost: 80 × EUR 250 = EUR 20,000 excl. VAT a month, i.e. EUR 240,000 a year.
- Target multi-tenant cost: 80 × EUR 60 = EUR 4,800 excl. VAT a month, i.e. EUR 57,600 a year.
- Infrastructure saving: about EUR 182,000 a year, before even counting time saved on deployments.
- Rebuild budget: EUR 120,000 excl. VAT over 9 months.
- Payback: about 8 months after all clients are migrated.
The real saving depends on migration pace: plan for 6 months of dual running during which both models coexist.
FAQ
Is a shared database secure enough for demanding clients?
With row level security enforced by PostgreSQL, automated isolation tests and an annual penetration test of EUR 5,000 to 10,000 excl. VAT, it meets most requirements. Clients that require physical isolation move to the dedicated database offer.
Do we need to rewrite the whole product?
Rarely. In most cases, 60 to 80% of the business code is kept, and the rebuild covers data access, authentication, configuration and deployment.
How much does adding SAML SSO alone cost?
EUR 8,000 to 18,000 excl. VAT depending on the number of identity providers to test (Entra ID, Okta, Google Workspace). Managed authentication services also exist, around USD 100 to 250 per SSO connection per month.
How do we migrate clients without downtime?
In waves of 10 to 15 clients, with a dry run, volume checks and an overnight cutover. Each wave takes 2 to 3 weeks.
Can we keep some clients on a specific version?
It is not recommended. Customisation goes through settings and modules toggled per tenant, which avoids going back to the 5 to 15 parallel versions that cost so much.
Let's scope your project. Tell us about your current architecture, your number of clients and your enterprise requirements: we will scope the multi-tenant model with an indicative budget and a 6 to 12 month 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.
