Two lines with different slopes
Subscription cost scales with people; build cost scales with scope. Where the two cross depends on your headcount and your vendor's price list, so there is no honest industry benchmark — a figure you find online is usually somebody's marketing. Both numbers you need are on documents you already own.
The cheap seats
The seats that catch operators out are rarely the power users. They are the field crew logging hours, the seasonal hire, the dealer who logs in twice a year. Contractor OS names seven organisation roles in its schema — owner, admin, project manager, estimator, accountant, field and viewer — and the last two are exactly the seats a per-seat bill counts the same as the rest.
Several businesses multiply it
Per seat, per tool, per entity. Business OS exists because eleven businesses on eleven stacks meant eleven logins, eleven bills and no consolidated view; it now runs them behind a single identity provider.
What to do about it
Do not answer the whole platform question at once. Start with the piece where the seat count is least connected to the work, and replace that. The full guide walks through the comparison.