Here's a feed I made for my buddy's band. It cost me 5000 sats, and that was a few years ago, so maybe $3. I think I have 10 years of hosting on it from satellite.earth. Check the links to the mp3 and image, you'll see it's all hosted on satellite.earth. If you plan on ever changing the feed, it needs to be at an address where the file contents can change without changing the file name, so a Blossom server may not be the best solution... yet. That's why I hosted the actual RSS on github, for free.

Image, mp3, RSS feed, it's all you need. Super easy.