The endless amount of Chinese Android-based single purpose mp3 player devices that are obviously iPod Nano/Classic clones basically cost ~$30 and have 50hr+ of battery life. You don't have to think about what player app to use, they ship with the only one that runs. The rest of the Androidness is stripped out.

Then yes, there's obviously the other end of the extreme where the mp3 player is very obviously a phone without a radio with a price tag to match. And everything in-between.

I'd say there's actually too many choices cause the silicon and battery cost required to simply play music has gotten so cheap that it doesn't make sense to optimize the OS further than Android. I'm sure the economics of scale means the actual hardware wouldn't be cheaper by any noticeable amount either.