For just $29 (for the first year, and $49 a year after that) you can upload your music to Tunecore, and they will distribute it for sale in all the digital music stores usually within a few days, and then collect all the sales revenue on your behalf. You can then withdraw the money you earn direct into your bank account.
The amount you earn from selling individual songs and albums seems to vary a lot, depending on which music store the buyer uses, and which country they live in. We seem to earn between $0.70-1.05 per download from iTunes, and maybe about half a cent per stream on Spotify.
Overall, it doesn’t bring a huge amount of money each year – maybe a few hundred dollars – but then again we’re selling choral music, which has a more narrow audience. However, it more than covers the costs of using the service, and earns us money with no ongoing effort. Plus it’s a great way to promote your music, and gives you a more professional image.