The bill that grows faster than your team
Every new hire that touches a per-seat SaaS tool is a line item that appears the same month they join. Hire five people in Q1, your invoice jumps in Q1. That predictability sounds fair until you remember that the vendor also raises the list price each year — typically 8–12% — and the two forces compound on top of each other. A team that grows from 20 to 40 people over three years while the vendor raises prices 10% annually does not pay double. It pays closer to two-and-a-half times the original bill. The ratchet only turns one way: upward.
The maths most finance teams miss
Take a realistic example: a project-management or field-service tool at £30 per seat per month, used by 20 people. Year-one cost: £7,200. Now apply 10% annual price increases and model headcount growing to 28 in year two, 36 in year three, 42 in year four, and 48 by year five. The cumulative five-year spend lands at roughly £53,000 — and that is before any enterprise tier upsell, additional module fees, or SSO/API add-ons. Most finance teams approve the first invoice and revisit the line item only when it has already become painful. By then, switching costs are high and the negotiating position is weak.
The ownership gap
After five years of payments you own exactly nothing. Your data sits in the vendor's cloud under their terms. If they decide to deprecate a feature, bundle it into a higher tier, or sell the company, you find out the same day as everyone else. Data portability is often technically possible but practically cumbersome — exports in formats that need cleaning, field mappings that break your reporting, historical records that lose their relationships. The vendor has every incentive to make leaving feel expensive and time-consuming, because the exit friction is part of the pricing model.
The exit cost
Switching a SaaS tool is rarely just a subscription cancellation. There is a contract wind-down period (often 30–90 days notice), a data-export window that may be time-limited after cancellation, institutional knowledge that lives in the tool's own structure (custom fields, workflow automations, naming conventions that only make sense inside that product), and the productivity dip during migration. Teams that have used a tool for three or more years frequently report that the knowledge-loss risk alone delays the decision to switch by another year or two. Meanwhile, the bill keeps running.
What the crossover looks like
Against that five-year SaaS spend, a co-funded custom build looks very different. Using the same £30/seat/month tool example: a purpose-built replacement for the 20–50 people workflow runs roughly £8,000 as a founding-five share of the build cost, plus £3,000 per year for hosting, maintenance, and support. Total five-year cost: around £23,000 — versus the £53,000 of compounding SaaS rent. The break-even typically arrives between months 12 and 18. After that, every year is pure saving, and headcount additions cost nothing extra because the fee is per-company, not per-seat.
Stop paying the per-seat tax. Co-found a build.
The compounding arithmetic of per-seat SaaS is a tax on growth. Every hire makes the bill bigger; every year makes the exit harder. Co-funding a replacement with four other companies in the same situation turns a prohibitive upfront cost into a fraction — and converts a perpetual rent into a flat annual fee you control. Your data stays yours, on a perpetual, escrow-backed licence, and the price is fixed for ten years. The maths works. The question is how many more years you want to keep paying for the same answer.