I'm another Pentacon Six user. You could try Cupog on the auction site who sells CLA'd bodies and lenses, plus frequently the meterless prisms too (much more compact than the metered version). The standard focus-hood is a bit too open and lets in a lot of extra on to the screen, so a bit of black card, folded to go around the outside of the hood, can help a lot to reduce the dazzle.
Rick Oleson sells brighter screens, with centre focus aid. Those work fine and are more than a stop brighter.
Assuming the body is in decent mechanical shape, the wind-on 'problem' seems to often be because people forget to have the film/backing-paper tight. That causes overlaps because the film-counter is based on a friction-driven wheel running on the surface of the film. If it isn't tight then it doesn't touch and/or slips.
There is lots of very useful information on
www.pentaconsix.com for further reading.
I found the screen from the Kievs can be cut down and fitted to the Pentacon, and they are perhaps the best thing the Soviets made as part of those systems.
The shutters of the Pentacon can do some odd things, I have had one that seemed OK, but the 125 setting was Bulb.
The advance mechanism was always a concern, with over lapping frames common, am not sure how they fixed them, but I quite often got a small plastic bag with broken parts back with the camera. It used to be a $30 repair for an overhaul in Prague. I was also told to never touch the tension fingers on the back, it just got to be too finicky for me, so when someone wanted the last one I had on hand, I shipped it to him.
I heard the Exactas were made in the same factory as the Pentacons.
I probably have a dozen adapters for various lenses for the Pentacon Mount, including a LTM to Pentacon, only works for macro, ;-)
I probably have adapters somewhere for Pentacon to Nikon F, Pentax K, Mamiya 645, and Pentax 645, plus one which is a remains to be seen as it was miss marked on the package.
They are fun, but when they break they are a pita to have serviced this side of the pond.
Too bad, as the glass for them is good and not very expensive, if I want to use them, I dig out a Mamiya 645 body + the adapter.
Local shop once gave me a lens for one because I was the only one who could identify the camera it matched. ;-)
I think there are too many other more reliable options.
I would stick with the Rollei, or hang around photo shows, occasionally a nice system comes in, in fitted case, of a Bronica, or Mamiya 645 with three lenses for well within your budget and presents a target of opportunity.
Regards, John