Typically such things are bootstrapped not by a wealthy user base but by a talented user base who write the code and set up the organization themselves.

However, if you do need some money for boostrapping, there are likely unions out there that would be willing to grant/lend the sums needed, which should be five figures.

Taking VC money would be counter-productive, making you beholden to conflicting interests.

P.S. The motivation for setting something like this up doesn't necessarily need to be purely selfless. It's not going to make you a billionaire, but if successful a non-profit or co-op you set up to do this can pay you a six figure salary for a job that has significant meaningfulness and significant agency (aka control over your own work). And by being a non-profit or co-op the lack of conflict of interest should make it more likely to be successful.