thanks for all your replies.
I mentioned I want spot metering, but what I really meant was being able to meter individual areas. So anything resembling spot metering or partial metering would be fine. I'm not too sure how these old cameras meter, and how centrally weighted they are. Maybe centre weighted average is all I need!
Most cameras used some form of center weighed averaging. Very few (like one year of the Nikon F) used flat full scene metering. Honestly, you'll be good with any of them.
I'm thinking hard about the FM2n at this point. I see that Afghan girl was shot with this camera. My portraits never come out as good as that photo, so maybe I should get this camera...
The camera had about 1% influence on that photo. Seriously. Steve McCurry could have shot that with pretty much any of the cameras listed here so far and no one would be able to tell the difference. Was his gear good? Yes, and he knew how to use it. What is really important (and is true for most other famous photos) is the light, the setup, and in the interaction with the subject. IE the person behind the camera.
Can someone explain soemthing - I understand the FM2 is mechanical, and FE2 is electronic. Yet FM2 has an LED meter, but FE2 has a physical needle? I find that confusing. I'd assume mechanical would have a needle and electronic would have leds. Clearly I'm missing something!
Re. price. Yes the FM3a isn't that expensive in absolute terms, but I'd rather spend ~$200 than ~$600 if possible!
Mechanical vs Electronic in this case only refers to the shutter timing mechanism. One is clock-work, one is an electronic timer and magnetic solenoid. As has been mentioned, don't fret about it. Batteries are easy to get, cheap, and light (in the canon AE-1 they last dozens and dozens of rolls, even the OM-2S, the battery pig that it is, gets 10 rolls on a pair of $2 batteries that take up less space than a quarter in your camera bag). I have romantic notions about mechanical shutters, but all my "go to" cameras are electronic, go figure.
When looking at your camera purchase, you're really buying into the lenses too. Nikon lenses tend to be expensive, because you can still use them directly on (higher end) modern Nikon digital bodies. Canon FD (AE-1) and Olympus tend to be cheaper because they have to be adapted. Pentax, despite being directly mountable on current Pentax digital bodies still seem to be cheap too (probably because Pentax doesn't have much market share right now).
For $200 you can get very clean camera with at couple of primes (28 and 50 for sure, maybe a 135 too) for FD, OM, Pentax K, or M42 off your local classifieds. Heck, on my local classifieds I could do most of those for under $100 right now. Nikon might be a bit more, but not enough to stop you from buying Nikon if those are the cameras that appeal to you. If you want the comfort that comes with buying from a place like KEH with a solid return policy, the price goes up, but you know what you are getting.