At 78. I've looked at a lot of MF folders and owned more than a few. My reasoning, first noting that they are all in the range of 70 years old, and by their folding nature, have been vulnerable to more wear and tear, as well as physical injury, than any other type of camera:
Skip the Super Ikontas. They use a complex optical rangefinder system which is imposed by its front lens cell focusing, is rugged, but difficult to clean and repair. Front cell focusing isn't a dealbreaker, but is an optical negative, everything else being equal. Durable build, but very heavy for the type of camera.
Mamyia Six. Many variations over a ten+ year production with many subtle variations in desgn of functions, shutters and lenses. Stick to the later (Automat) versions, with square rangefinder window replacing the earlier round window with bezel. Get one with the Sekor lens. The Olympus lens has some brand attraction, but the stories about their lens failures are quite true. For Mamiya, Oly used an inferior grade of glass and coatings which failed with age. They develop a heavy haze which cannot be cleaned off, making photos which look like they were shot through a gauze screen. There is a terrific YT video where a new purchaser of one such Mamiya Six shot his Mediterranean vacation, getting a cross-section of such photos. Very sad.
Much better option in a folder: Konica Pearl III, 645 format; 75mm 3.5, in the middle of your budget. Nearly the perfect 645 folder behind the Pearl IV, which is vastly beyond your budget.
Much better option, non-folder:: TLR: Rolleicord (post-war). Ricoh Diacord G or L (not the 225 model or earlier Ricoh TLRs); [Absolutely Not a Yashicamat, any model, no exceptions.]
There are no 6x9 folders in your budget which are not clumsy old antiques.