Finder repairs can be cheap or expensive depends what is wrong.
If you use a standard lens exclusively the M3 is nicer, it you use a widerangle sometimes the M2 is necessary, there is a kludge (for M3) but it is horrible.
The M2 finder was cheaper to make but all the later cameras use it, even the latest MP and M7 although they have hard coated surfaces.
The Canon P is in many ways more practical but it only takes screw thread lenses.
Assuming you are like me and strongly prefer non-metered Ms, these are my thoughts. I think if you have only one M, then the M2 is the best all-round in terms of quality and price. (You can sometimes find the M4-2 for roughly the same price as a M2, but the VF is not as flare resistant as the M2's VF.) The M2 is a great all-round camera with the classic 35-50-90 framelines. If you can afford a bit more money, then the M4 does what the standard M2 does, but is a tad bit faster in use: with a M4 you get the faster tulip film loading and the slightly faster angled film rewind.
But if you are dedicated to the 50mm focal length, I would recommend what others have suggested: get a M3 and go to it!
Any of the classic Ms rock; so pick one of the M2-3-4s and you will be glad.
"A great civilization is not conquered from without until it has destroyed itself from within." W. Durant
I sent my old single stroke M3 to Peter at CRR Luton for dull and low contrast range finder, it came back like new. He's can actually re-sliver prism's if necessary, mine didn't require. The only issue is he's booked a long time into the future, July now.
Well, I had both. My answer? F2! (Where's the emoticon for "ducking for cover" when you need one?)