Someone on the Pentax forums has asked me for recommendations for a really cheap 50mm lens to fit a Nikon D7000, for a friend who has never used a prime lens - the trouble is that (unlike Pentax) there really aren't many alternatives to Nikon, especially not cheap ones. I ended up suggesting the Series E manual 50mm and the older AF 50mm D, which aren't exactly cheap but probably won't break the bank. The only other idea I could come up with was a 50mm M42 lens with adapter, but you've got the complications there of either not focusing to infinity, or losing a little quality.
Am I forgetting some other source? Did anyone else make Nikon compatible 50mm lenses that aren't completely horrible and might suit his needs?