WOOT.com has 1GB MP3 players on sale for $6.99. They are for Disney shows, but that shouldn't matter if you are putting them in props. Besides there is something to be said about having a Hannah Montana mp3 player in a zombie prop.

Coupon code ONEBAG will get you $5 off.

sorry for some reason the coupon code didn't work for my wife. I apologize if it doesn't work for you. Maybe it was something specific to my woot account.