Depends what you mean by a decent one socci!
I'm not an expert on mp3 players, but there are basically two kinds - the little, smaller capacity ones (128Mb or 256Mb) or the larger capacity "jukebox" type ones (like ipods).
The smaller capacity ones are great - i've got a little phillips one that is rechargeable. Holds about 4 albums' worth of tracks. Light and easy to use. Costs under £100.