If you're looking for an alphabet cam, I think the best place to get one would probably be Craigslist or Marketplace. I don't know if I'd spend the money on new. For example, a couple years ago I picked up a FMS "B" cam off of CL for maybe $50. You'll definitely need to be in the right place at the right time though....
I'd suggest settling on what heads you'd like to get and buy the corresponding parts according to their characteristics. If you've got the time, I think this video will help explain why I say that.