I dis the same when I got my M4. Started with a Jupiter 12, which I stupidely sold when I could afford a Zeiss Biogon.If it were me I would get an FSU lens for next to nothing - letting you use the camera - and save up for the DR Summicron.
Jupiter 12 or 8 cost next to nothing and you will enjoy the M3 until you can get a better lens.