There are a few bounty-based services out there
https://gitpay.me (Poor adoption; Bad behavior in the past by enrolling developers without permission)
https://www.bountysource.com (Started keeping expired bounties; Sold to cryptocurrency company)
https://issuehunt.io (Not sure about this one. Seems to have some traction: https://issuehunt.io/r)
but I'm looking for something that puts the developer in control by allowing them to request payment on feature request issues in Github. It could be as simple as adding a "Pay Now" button to the issue.
Doesn't appear to be too popular: "We paid $2547 USD in bounties". And no wonder it's not popular: https://github.com/gitpay/website/pull/4
The docs are pretty thin, so it's not clear if it's possible for devs to attach a price to feature requests themselves.
It seems to be a side project of the people that make Boost Note. The top project has gotten $7,858.50, but it's actually their own project BoostIO/Boostnote. I get that "we made it for us, but you can use it too" vibe from their site, which may be why there doesn't seem to be much ongoing effort to promote the service.
It looks like there are red flags around Bountysource:
https://blog.elementary.io/goodbye-bountysource-hello-github...
"If no Solution is accepted within two years after a Bounty is posted, then the Bounty will be withdrawn and the amount posted for the Bounty will be retained by Bountysource."
"In December, 2017, Bountysource was acquired by a cryptocurrency company called CanYa who redesigned the Bountysource site and service with a new cryptocoin focus."
[1] https://docs.github.com/en/free-pro-team@latest/github/build...