The often-rebranded Cosina and Tokina 24s are often available cheaply in some mounts. Minoltas sometimes, because not many people are using the MD lenses anymore. Pentax, not so much. This is a good example to illustrate the trade-offs of vintage systems; some, like the M42 and K-mount, have oodles of lenses available, which drives prices down in some cases but not across the board because these are also still easily usable on digital cameras. Depends on particular lenses, and there's not always a correlation to quality (just what's either a well-known "classic" or a current fad).
Originally Posted by darinwc