Hello - This Blackhawk was mfg in 1957, 3rd year of mfg. You can get yom info on Rugers from their website at:
http://ruger.com/Firearms/PS-SerialNumberHistory.html .
These older .357 Blackhawks are quite sought after because the frame size is smaller and lighter than the .44's, unlike the New Models. You can get a realistic sale price value by monitoring auction sites, such as gunbroker.com or gunsamerica.com .