As a collectible, the price varies non-linearly with condition; there are some rare-ish variations that can boost the value; and the presence of original extras like caps and case can be significant. A mint condition lens in a rare variation with caps could go to $600.
If it's a user lens (i.e., cosmetics not pristine, not a rare variation), then the optical/mechanical condition of the lens and how recently it was last serviced are paramount. From $150 for a flea market find to $400 for one with a recent CLA and clean glass.