I also have a Spotmatic in the bottom drawer, unfortunately the then expensive screw lenses are not going to help much on a modern camera, although they will sort of work with an adapter.
I have just got a Pentax *ist DL to supplement my Pentax SFXn’s. It takes all my old Pentax FA/KAF lenses with a 50% increase in focal length but no loss in speed so my 50mm F1.7 is now a very useful 75mm F1.7 and a 70-300mm F4/F5.6 APO is now great 95-450mm F4/5.6!.
Initial impressions are excellent and it drives my old Pentax & Metz dedicated flash guns correctly as well, automatically correcting for the different focal length.
I sold a Bronica kit on e-bay with no problems, I think many of the vendors (and my buyer) are dealers, a check on their history may tell you. I noticed in UK there are a lot of personal imports from HK (particularly Pentax *ist S) boxed etc, not sure if I’d trust them.
Most will be a lot cheaper in the US, Hong Kong etc, an internet search of the deals is worth while. The Pentax would probably come around the budget in a US discount store but don't forget to add the price of a memory card!
Good luck and happy snapping!
Will now be selling my Nikon CoolPix 995 compact on e-bay, hope it goes as well as the Bronica.