The super cheap way to do it is to get vinyl from your hardware store. It is very near the same material as the screen protectors are, and is insanely cheap. You can buy enough vinyl to make probably 20 protectors for like $1.
I did this a long time ago with a PDA and the protector worked great. It fit on great and did not degrade the screen quality at all. When it came time to sell my PDA, I peeled off the protector and the screen was in pristine condition.
The 2 drawbacks to this are
1) You have to be pretty exact with your cutting else it may not fit perfectly
2) I recall it being more difficult to apply the homemade protector to my PDA screen than it was to apply my Pelican DS screen protector. Maybe it was a different material, maybe there was some kind of coating on either the protector or the DS screen itself, but I remember it was a little trickier to get a good application on my PDA screen. The benefit is that once you put it on right, you don't ever need to take it off again.
Ruahrc
P.S. Post #100. W00t! Now when do I lose my CAG-In-Training status? Is it a post count thing or a time-registered thing?