Ask HN: At what stage did your company move from 3rd party to internal software?

Because that $15K for 6000 users is not about the cost to build the app. It is about saving the cost of internal staff to maintain the app. Even if you end up with 10 apps at $15K, the cost of the internal IT talent to maintain it is probably still more expensive, unless you find the miracle employee who can be a one-man wrecking crew for 10 different solutions, including the DevOps and other functions to support reliable operations and business continuity for all the apps. (24 x 7, too.)

I'd say that even if you do have an internal IT dev staff who could take it on... don't. Their efforts are better spent on things that are unique to your business, not re-inventing wheels.

At a company, we would stick a team of up to 3 devs + manager on an internal product to replace or create something we wanted but didn't want to pay for. That cost is R&D (so taxed differently -- ammortized) so it would often be magnitudes in less cost than paying for a product, unless the product did something we conceivably couldn't build or only a small number of users would be using (such as on-premises BI tools).