Check post in the last week; someone else asked the same question. I have it and use the 50mm CF fairly often; it depends on the subject and the surroundings.
I'd guess something like $US750-850. Prices seem to have dropped a little recently on most Hassy lenses - especially the 150 Sonnar for some reason (at least here in Australia). Ex grade CF 50's go for about A$800 here. Try KEH for a good price comparison.
I too am thinking about selling my 50mm CF Distagon and was curious about pricing. I think the demand may be driving prices down. I've been watching 'that auction site' and interestingly, they just don't seem to be selling.
Not quite sure if it's due to the demand for film camera equipment overall, the focal length of the lens, too much supply, or what....
I too have been looking for a clean 50 CF. I have a 40, an older T* that is somewhat too wide on some shoots. Its a filter or hood thing that gets me with the T* 40.
I hope to limit my filter and hood choices by adding a 50 to my colection (40, 80, 120 & 150) So this is junkie speak for I have to have more. More, MORE!