Richard Cochran , Aug 02, 2003; 12:53 p.m.
You're probably actually shopping for an FM2n, not an original FM2 (the FM2 had a very short production life, and is somewhat rare). The difference between the FM2n and FM2 is that the FM2 has 1/200 flash sync, while the FM2n has 1/250 flash sync.
Anyway, I own an FM which I purchased in 1980, and an FM2n which I bought in 2001, 21 years later. The differences are small, most significantly in the max shutter speed and flash sync speed. The FM is in many ways a better camera, including compatibility with non-AI lenses, and more parts made of metal where the FM2n is plastic. Of course, my FM also has an extra 21 years of wear on it, and I suspect that sort of thing accounts for much of the price difference between the models.
I examined my two cameras side by side and described all the differences I could notice on this web page. Note that most of the differences noted are cosmetic with no real significance.