I recently come across a similar question on Reddit. While I can't offer the company perspective I can offer a maintainer perspective:
https://www.reddit.com/r/opensource/comments/rwmiwn/recommen...?
https://www.reddit.com/r/opensource/comments/rwmiwn/recommen...?
Really if we’re honest, any company using Bookstack should be able to afford to chuck you $20/month or something (barring perhaps one-person bootstrapped startups). It’s likely red tape, bureaucracy and the internal culture that prevents this more than financial means.
And especially so if support demands are being made of you!
Getting approval to throw an open source project some money is likely to be even crazier (probably not a concept they ever imagined).