Well you don't have to use Leitz lenses. Zeiss, Voigtlander also make M-mount lenses. Overall excellent and much more affordable. Also, Leica screw mount lense

Well you don't have to use Leitz lenses. Zeiss, Voigtlander also make M-mount lenses. Overall excellent and much more affordable. Also, Leica screw mount lenses + M39-to-M adapter is also a great option :D