Not a totally crazy idea. I've seen cars with such a display in to accompany the graphic one (stock though). If you have programming skills and can access the API of a regular GPS package, then I don't see why you couldn't output to an LCD module. I assume you would also need some sort of driver module plugged into a serial port. Sure I've read about these somewhere.
Not sure how useful this reply is really since there are no real answers or links. Perhaps I need to stop chewing pencils also.