The Hidden Costs of SaaS Subscriptions vs. Building Your Own Platform
SaaS pricing looks straightforward until you grow. The compounding costs of licences, per-seat fees, and feature tiers often make a custom platform the more economical choice at scale.
SaaS Costs Are Rarely What They Appear
The initial appeal of SaaS is transparent pricing: a predictable monthly or annual fee that makes budgeting simple. But as organisations grow and their SaaS stacks mature, the total cost of software licencing frequently becomes a significant and poorly understood line item, often the second or third largest operational expenditure after payroll.
The Hidden Cost Layers in SaaS
Per-Seat Escalation
Most SaaS products price per user. At 10 users, this is manageable. At 200 users, per-seat pricing for five or six tools creates a monthly bill that would fund two full-time engineers.
A hypothetical mid-size company with 150 users:
- CRM (Salesforce): £75/user = £11,250/month
- Project management (Jira Software): £8/user = £1,200/month
- HR platform (BambooHR): £6/user = £900/month
- Communication (Slack Pro): £7.25/user = £1,087/month
- BI tool (Tableau): £42/user = £6,300/month
Total: £20,737/month (£248,844/year), for five tools.
Feature Tier Lock-in
SaaS products typically gate the features organisations actually need behind enterprise tiers that are 3–5× the standard price. SSO alone is frequently locked behind enterprise pricing, creating a security liability for organisations that cannot justify the cost uplift.
Integration Tax
Connecting SaaS tools to each other and to internal systems requires either expensive native integrations, middleware platforms (Zapier, Make) with their own per-operation pricing, or engineering effort to maintain custom integrations that break with every platform update.
Data Egress and API Costs
Moving data out of SaaS platforms (for analytics, backup, or migration) incurs costs that are often buried in small print. At scale, these become significant.
Vendor Lock-in Exit Costs
When you eventually migrate away from a SaaS platform, the cost is not just the new licence, it is data migration, retraining, integration rebuilding, and the productivity loss during transition. These exit costs are never included in the initial TCO analysis.
When Building Your Own Becomes Economical
The crossover point, where the cost of building and maintaining a custom platform is lower than the compounding cost of SaaS licences, is typically reached when:
- Annual SaaS spend on a category exceeds £80,000
- The platform is core to competitive operations (not commodity function)
- Per-seat pricing is growing with your headcount in a way that becomes prohibitive
- Integration complexity between SaaS tools has become an engineering burden
At these thresholds, a custom platform that costs £150,000–£250,000 to build and £30,000 annually to maintain becomes cash-flow positive within 2–3 years.
A Framework for the Decision
Stay with SaaS when: The function is commodity, your organisation is small, or you lack the internal capability to manage a custom system.
Build custom when: The function is core to your competitive operations, per-seat costs at scale are prohibitive, your requirements exceed what SaaS offers, or you need data control that SaaS cannot provide.
Hybrid: Use SaaS for commodity functions (email, calendar, payroll) and build custom for the systems that differentiate your operations.
Conclusion
SaaS TCO analysis over a 5-year horizon frequently tells a very different story from the initial per-seat price. Before committing to a SaaS platform for a core business function, model the cost at 2×, 5×, and 10× your current scale. The build-vs-buy inflection point arrives faster than most organisations expect.