There have been some other brands for which you could get new touch screens and screens and replace them yourself. I doubt the channels for Dell have them in stock yet, but if you could find out the model, you might be able to get one cheaper than replacing the whole unit. I also saw on
here pictures of the inside of the unit, and this thread a Dell discusses the innards:
Dell thread.
If you take the serial number on the screen and check with a parts supplier, maybe
PocketPCTechs, they might be able to repair/replace the screen for you. It's a longshot, but unfortunately at this point you have very little to lose.