When my son became interested in photography I purchased a Vivitar 70-150 for $10 from an "as is" box at the camera store after running a short test roll through it. It was in very good condition and the glass was perfect. I recalled its reputation, and having sold a number of them. Contrast isn't terribly high, but overall performance is most certainly serviceable. About 6 months later my son found a 135 f:2.8 MC Rokkor in mint condition for $40 and fell in love with that, so the 70-150 hasn't seen much service lately.

Lee