You want to do medium format on a budget. For 645 format either a Bronica Etr, Etrs, or Etrsi, with a 75mm, then add a 40 or 50mm wide-angle and a 150mm tele. Bronicas are dirt cheap right now. For 6 x 7 format an Mamiya RB 67 Pro S all mechanical, built like a tank. Lenses are excellent, and being given away for what they are worth. Another option is the Pentax 6 x 7 with an assortment of lenses. Not as good a bargain as the Mamiya but the body and lenses are excellent. For square format a Rollei MX or MX-EVS with either a Tessar or Xenar lens. Both will render sharp contrasty images. Hasselblads are pricey but you can add to the system piece by piece and lens by lens as bargains crop up. Probably one of the best built of the medium format modular systems. Good luck with your search.