I hadn't considered the bluetooth/wireless route with a PDA as a solution. Here are a few links to some threads on the forum that offer a few economical ideas for backup cameras. I have also had some success with a wireless unit that I picked up at a Wal-Mart for $50, from a company called Astak at:
It comes with a color camera and receiver with a 300 ft. line-of-sight range. For the money, I was impressed with the quality of the unit.
Good luck, and if you go the bluetooth set up, let me know how it works out for you. In my case, I think a good backup camera system will go a long way in preserving domestic harmony.