Sounds like it may be more work than its worth. Those Ebay ones I think are priced pretty reasonable.
Have you looked into a waterproof MP3 player?? You can get waterproof housings for lots of them on the market today.
A friend of mine uses one of these:
He has it very well secured to the back of his suit and then runs the wire up under the back of the wetsuit. I do the same thing when I'm out hitting the big waves on the PWC.
