Uniform Motion details what they get to keep from various different methods of distributing their music:
>That being said, it costs us 35 EUR/year to keep an album on iTunes, Spotify, and Amazon (105 EUR per year for all 3 of our albums!) so we don’t make any money until 24 people have bought a digital copy of the album on iTunes, or 150 single songs, or if we get tens of thousands of listens on Spotify! In most cases, it’s actually more economically viable not to sell the music at all.

It’s a pretty amazing break down.