A used iPod (probably flashed with the open source Rockbox firmware) for the cool factor and reducing ewaste. This is an amazing guide: https://yuuiko.github.io/iPodGuide/iPodGuidev2-1.pdf that gives recommendations on what model and the mods you can do. I have a 5.5 gen with an SD card mod all for £50.

Edit: Actually, I forgot the eBay listing said it was a 5.5 gen but the serial number when I got it was just 5th gen, and I got a full refund! £20 in total then.