The first question is boring and it settles a lot of arguments. What are you actually paying?
Add up your real annual spend. Not the sticker price per seat. The fully loaded number. Licenses, add-on modules, the premium support tier, the connector you pay a third party for, and the consultant you call twice a year to fix your automations.
Say you have 12 people on a project platform at $30 per user per month. That's $4,320 a year. Even over five years, that's about $21,600. A custom replacement almost never pencils out against that. Stay put.
Now change the numbers. Say you have 85 users at $95 per month, plus a $22,000 annual platform fee, plus $18,000 a year for an integration partner. That's roughly $137,000 a year, and it climbs every renewal. Over five years you're near $700,000 with increases, and you own nothing at the end. That's a different conversation entirely.
The line isn't a fixed dollar amount. It's a ratio. If a build costs about the same as two or three years of subscription and you own the result forever, the math starts favoring the build. If it costs more than five or six years of your current spend, staying is the smarter move by a wide margin.
Ask your finance lead to pull three years of actual payments to the vendor, not the current contract. Most companies find 20 to 40 percent more spend than they expected, hiding in add-ons, overage charges, and consulting invoices coded to a different budget line.