John, the Jupiter 12 35mm lens won't fit on the psot war Contaxes. That means you're stuck with buying an expensive Zeiss Biogon or an expensive Nikkor 35 for Contax or Nikon. They are slightly different, (nikkor for Contax and Nikkor for Nikon) but the wide angle will provide enough DOF to eat up the focusing difference. The only other thing you can do, and this would be cheaper, is to buy a Kiev camera to use a J12 on.
The FSU J9, an 85 f2 lens, will fit and focus on your Contax so you won't have to buy the esxpensive Zeiss 85, or you can at least wait until you find a good deal on one.