The verdict in three sentences
At 300 customers, your isolation model sets your cost per tenant, from 2 GBP a month on a shared database to 25 GBP a month on a dedicated database. For most London B2B vendors, the best trade-off is schema-per-tenant isolation in PostgreSQL, with dedicated databases reserved for enterprise accounts that pay for them. On AWS or GCP, expect a cloud bill of 2,000 to 15,000 GBP a month depending on load, and a multi-tenant rebuild of 30,000 to 90,000 GBP.
The three isolation models compared
The decision is not a technical preference. It rests on three criteria: what customers require contractually, what each tenant costs and the operational load on your team.
| Criterion (300 tenants, 2026) | Shared database (tenant_id) | Schema per tenant | Database per tenant |
|---|---|---|---|
| Infrastructure cost per tenant | 2 to 4 GBP/month | 5 to 10 GBP/month | 15 to 25 GBP/month |
| Data isolation | Logical (RLS) | Strong, same instance | Physical |
| Per-customer backup and restore | Complex (filtered export) | Simple (pg_dump per schema) | Native |
| Schema migrations | 1 | 300, orchestrated | 300, slower |
| Noisy neighbour effect | High | Medium | None |
| Enterprise sales argument | Weak | Fair | Strong (ISO 27001, SOC 2) |
| Operational load | Low | Medium | High |
A shared database with Row Level Security is the cheapest, but one missing filter exposes one customer's data to another. Schema per tenant keeps one instance to monitor while letting you restore a single customer in minutes, which answers most buyer security questionnaires.
What hosting costs at 300 customers
Here is a 2026 monthly estimate for a mid-size B2B SaaS: containerised application, high-availability managed PostgreSQL, object storage, backups and monitoring. Estimates only, third-party licences excluded.
| Monthly item (schema per tenant) | AWS (London eu-west-2) | GCP (London europe-west2) | European provider (OVHcloud) |
|---|---|---|---|
| Application compute (managed Kubernetes) | 800 GBP | 760 GBP | 480 GBP |
| Managed PostgreSQL HA | 950 GBP | 900 GBP | 560 GBP |
| Object storage and 30-day backups | 220 GBP | 210 GBP | 120 GBP |
| Egress | 160 GBP | 170 GBP | low or included |
| Monitoring and logs | 180 GBP | 160 GBP | 130 GBP |
| Monthly total | 2,310 GBP | 2,200 GBP | 1,290 GBP |
| Cost per tenant | 7.7 GBP | 7.3 GBP | 4.3 GBP |
As data volume and traffic grow, the same architecture typically reaches 6,000 to 15,000 GBP a month for a few thousand active users per tenant. AWS and GCP keep real advantages: service breadth, compliance tooling (SOC 2 evidence, audit logs) and global regions. European providers are usually 30 to 40 % cheaper at equal load, mainly on managed databases and egress.
The budget for a multi-tenant rebuild
A rebuild touches code, database and operations. The ranges below reflect the 2026 London market, senior contractors or specialist agencies.
| Workstream | Indicative duration | Market range (GBP) |
|---|---|---|
| Audit and model choice | 2 to 3 weeks | 5,000 to 12,000 |
| Tenant layer (resolution, context, RLS or schemas) | 4 to 8 weeks | 10,000 to 30,000 |
| Per-tenant migration tooling | 2 to 4 weeks | 5,000 to 15,000 |
| Automated customer onboarding | 1 to 3 weeks | 3,000 to 10,000 |
| Per-customer backup and restore | 1 to 3 weeks | 3,000 to 10,000 |
| Infrastructure as code and cutover | 2 to 4 weeks | 4,000 to 13,000 |
| Total | 3 to 6 months | 30,000 to 90,000 |
At Kolonell, a complex SaaS application sits in the 7,000,000 to 15,000,000+ FCFA (10,670 to 22,870+ EUR) band of our grid, with maintenance from 120,000 FCFA a month (180 EUR) at Premium level.
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Oliver, CTO of a London HR software vendor (illustrative example), serves 20 customers on a shared AWS database at 1,700 GBP a month, or 85 GBP per tenant. He plans 300 customers within 24 months. Staying on AWS with schema per tenant, the bill would rise to about 2,310 GBP. A European provider would be close to 1,290 GBP.
Calculation: 1,020 GBP difference per month, or 12,240 GBP a year. He chooses to stay on AWS for its SOC 2 tooling, but moves to schema per tenant: per-tenant cost falls from 85 to 7.7 GBP, and isolated restores let him close two enterprise deals that required them.
FAQ
Which multi-tenant model fits a B2B SaaS?
Schema per tenant suits most B2B SaaS products with 50 to 2,000 customers, at 5 to 10 GBP per tenant per month. Beyond several thousand small customers, a shared database with RLS becomes more cost-effective again.
How much should a SaaS spend on cloud?
A common benchmark is 5 to 15 % of revenue. For a vendor at 300 customers, 2,000 to 15,000 GBP a month is a typical range depending on data volume.
Can the models be mixed?
Yes, hybrid is the most common setup: schemas for most customers, a dedicated database billed 300 to 1,000 GBP extra per month for demanding enterprise accounts.
How long does a multi-tenant rebuild take?
Expect 3 to 6 months for 30,000 to 90,000 GBP, with customer-by-customer cutover to avoid downtime.
Does UK GDPR require a database per customer?
No, UK GDPR does not mandate a specific isolation model. It requires appropriate measures: encryption, access control, logging and the ability to delete a customer's data on request.
Let's scope your project. Tell us your current and target customer count, your stack and your security requirements, and we will propose an isolation model, a rebuild budget and a timeline. 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.
