I have the opportunity to travel around a lot for work... I recently while killing time in a strange city went into a pawn shop...
The shop owner had an old old camera with a screw mount 50mm macro Takumar lens.
I tested it out as much as possible and I determined the lens would be 'useable'...it had oil all over the mount and the aperture blades were rusty but they worked fine.
He wanted $50 for it but I didn't go for it...mainly because I had no use for the lens and plus I wasn't into it or informed on it. The guy was selling it as an 'antique' so if I want it I can go get it... the optics I would classify as 'so so' because it had dust on it....
I passed on that buy...but if I want it I can go back tomorrow and get it possibly.
HOWEVER....I saw a SMC Pentax-A 50mm 1:1.7.
I paid $10.
Front and rear caps. MINT condition.
I came back to my hotel and put it on the camera and it works beautifully. It was in a case and had obviously been taken care of.