Help! I don't know what mp3 players should I buy for my third graders!

I have recently received a $500 grant for mp3 players and audio books for my classroom. I am hoping to have my students create podcasts of book reviews and reader's theater performances along with the audio books. I am looking for advice on what to buy that will stand up to 8 year old daily use and abuse and still keep on running. I am fairly new to this tech stuff and it is my first grant. Any suggestions?