The bounty model only works when a few individuals (businesses in that case) are very interested in the result. I'm not aware of any projects that run on a bounty model and also take small payment from thousands of sources to make it happen. Unless you have some super-fans willing to drop a lot of money, or price your bounty incredibly low [0], I don't see this working for a song.
The alternative solution doesn't address the above commenter's problem that you shouldn't charge for copies of music, but for the creation of it in the first place.
[0] And yeah, I realize expecting a high bounty is kind of hypocritical for an indie musician. I've made maybe $50 from my music sales/streaming over the past decade, so why should I be asking a bounty bigger than a few dollars for any song? Well, because with the bounty model I'm setting a ceiling for what I can earn from my work, which doesn't exist on a pay-each-download model. Maybe over the next 10 years I'll only earn another $50 from music, maybe I won't, but I don't want to lock that in.
Also, I am going to make my music regardless of any sort of bounty. The payment is just for whether or not I release the music. Open Source projects typically use the bounty to pay a developer to work on the project. They don't develop an entire project and then withhold release until they get payment. Software doing it feels necessary. A musician doing it feels stingy. It just doesn't feel like a comparable model to me.