I paid $550 shipped for an HP (pre 28) 11 years ago, so I don't think that $600 today is out of line. Mine is a 5 screw serial number S 1291XX that shipped in 4 of 1955. Since the HP was introduced on April 15, 1954, mine is either a late first year gun or an early 2nd year gun.
It is also interesting to note that your gun is model marked, however, the box is not. Just goes to show that S&W did not throw anything away and obviously used up all of their HP boxes before they began shipping in boxes marked Model 28. Mine resides in a non marked box serialed to a gun produced somewhat later with an S 147XXX serial number written on the bottom. The box has no exterior markings but has a printed white label on one end.
