I bought an FM2n new in the mid 90's and paid that or more for it and that was just the body. Considering inflation, you got a good deal. I paid about $700 for an F3HP a couple of years ago in virtually NOS condition (new, old stock). Pristine, and I haven't regretted that, either. You made a good choice.
The only thing the FM3 has that the FM2n doesn't have that I would like, is mirror lockup. (Yes, the F3 has other features, but I they are not important to me.) But, if you use the self timer on the FM2n, the mirror goes up when the shutter release is pressed, the timer times down, and then the shutter releases, so it's sort of a mirror lockup. I prefer the general feel of the F3, including the additional weight, but I still like the FM2n.