LyX has some kind of mechanism for jointly donating towards the implementation of a specific feature.

With a bit of googling there seem to be quite a number of sites for
arranging freelance work like this. I don't know if anyone here has an
experience with such a site or would be able to recommend one, but my
guess would be that it might be easiest and most transparent to just
post your requests on such a site and announce it here, especially if
you also want to let others donate.

Med vänlig hälsning,
Björn A. Göransson