As others have pointed out, platforms to fund work on open source projects already exist, and the best part is: they're open source themselves, so you can contribute! In fact I was the top developer of Gratipay for a year myself, and now I've created a fork called Liberapay (the reasons were the legal difficulties Gratipay faced in the US, and the decision its founder made to turn it into a non-neutral platform).

Links:

https://liberapay.com/ https://github.com/liberapay/liberapay.com (Python)

https://gratipay.com/ https://github.com/gratipay/gratipay.com (Python)

https://salt.bountysource.com/ https://github.com/bountysource/core (Ruby)

https://snowdrift.coop/ (not operational) https://git.snowdrift.coop/sd/snowdrift (Haskell)