>>2940581M3 is a great camera but if you primarily use 35mm lenses, go with an M2, or M4 (M4, M4-2, M4p).
going with an old leica, budget for a CLA within a year. That could be anywhere from $250 no replacement of worn parts, more for a guy who will replace parts with good used parts, all the way to $1000 for sending it to Leica in Germany, who will re-manufacture any worn parts that are no longer available.
I went with the Germany rout for my M3 and got a full report of all repairs, basically it is a brand new camera.