I really enjoy using my super ikonta iv, i got mine pretty cheap because of lens fungus and super stiff focusing, but I took it apart and cleaned it (most of it as i could not get the front element out due to two previously stripped tiny set screws of the three on the front). I removed the large portion of fungus in the back and now even with the little bit in the front still the tessar shoots amazingly well and sharp, and the focus is very smooth now, and well aligned with the range finder (which was also cleaned). selenium cell meter works too!
one of the most important things when getting a folder is to also check the bellows. repeated use and age may dry and crack them. you can only patch the so much, and replacements may be tricky to find.
another cheap route is to find the ikonta copies, there are lots of them out there, like some mentioned above. You could also research the olympus six which is a copy that at one point used a german tessar lens (prewar).