6x7 projectors are rare and expensive (Götschmann comes to my mind), but maybe not more expensive than a Hasselblad projector?
If you want to confine yourself to 6x6 than I would suggest one of the newer Rollei projectors (P66 series) with a GOOD lens (Schneider AV Xenotar, huge difference over the standard "Heidosmat" lens!). Stay away from the Rollei P11, as it is quite dim and takes bulbs that are difficult to source, IIRC. The Schneider Xenotar lenses are a bit rare but not impossible to get with a bit of patience. I don't worry too much about the future of slide film, I shoot color as long as it is available and then there will still be b&w slides.