I would say $350 to $500 depending on condition.
Most stainless .38spl J-frames go in the $400 to $450 range. The Model 60's usually go for $375 to $400. (Note that no-dash, pinned barreled Model 60's will go for significantly more.)
The no-lock, frame-mounted firing pin 637's usually go for sub $400 prices. However, I haven't seen a hammer mounted firing pin 637 at auction, so I don't know if it would go for more or not.