A nice idea, but you're going to find yourself in support hell faster than you can say "but I said no iterations". As soon as you develop anything for anyone you become their perpetual unpaid technology bitch, phoned at 4:30 AM to be asked how to reprogram the VCR or why minesweeper won't start up.

But seriously - whatever you do, make very, very, very sure that you have, in writing, a contract which explicitly states that once you deliver, you're done, or you'll end up in hell.