There are usually from 3-5 GIII's a week on the Goodwill Auction site. It is
Interestingly, almost every GIII I've purchased there has been a working example after a bit of cleanup and exercise. The way to exercise the GIII shutter is to sit for hours in front of the TV watching "bad" programs and cocking and shooting the camera on manual mode until the shutter starts working.
Rapid actions seems to warm the blades and they start opening. Just keep going.
I have also been known to use the Ronsonol Flush method to loosen up the gummy blades. (I know many find distaste with this method, and Ronsonol is NOT a lubricant, but the purpose is to get the camera functioning... They are just throwaway cameras anyway. You'll run a few rolls through it and bury it in yet another closet. Great shooters though, just no mystique or soul.)
Anyway... clean up and a set of light seals (very DIY) from Jon Goodman, and your in business. I wouldn't POP the TOP until you see what you get for a few bucks. Canon built these in the millions as I recall. The survivor rate is higher than most and more than some people posting here think. I have turned every one purchased at shopgoodwill into revenue... working and with good meters.
However, remember there are very few camera literate people working at Goodwill stores, so every one is a "pig in a poke".