For a tight but used 13-1 blue 4" I would go $450, 3" fairly rare I would go $550 if in good shape, maybe a bit more. Regional prices can vary, I have seen CA folks post $100 or more over others' guestimates often.
It is a nicely balanced gun with a sweet trigger.
Post the first 4-5 letters / numbers of the serial number folks here will give you a DOB. My 4" is from 1977.