I like the value add that TideLift does, but the minimum buy-in for TideLift was more than we were willing to spend as a small startup. I felt bummed that we weren't able to help.

No such problem here, though - expect me to signup very shortly :)

CFOs are more reluctant to pay for just straight up donations, which is why some projects sell "support", etc...

Your service is a great idea and I would love to see it take off - and I think you'd make it much easier for developers to get work to pay for a subscription if you provided some tangible feature in return.

Just start with something simple and completely automated - like license checking. Startup's don't generally do this initially, until at some point some compliance person makes them - and then the CTO needs to get someone to setup a bunch of tedious license grovelling stuff. No one wants to do it and it's annoying - people will pay for it.