Hello

Just a thought, go into a cell phone store and ask for an Anti-Glare screen protector for the largest phone they carry. Maybe look up who sells an android Tablet, or a Droid Evo ... ask for the anti-glare screen film.

If you can find one for a tablet, just cut it to fit.

If you find one for a smaller phone than your gps, just buy a few of them and make it work

cheap solution, i hope it helps.