S&W did some blackened SS guns for a HP department, several years ago- they would not refinish them, as the process was prohibitively expensive. Black chrome would be ok, as long as it is not a carry/much used piece- BC is roughly equal to electrloess nickle, in wear resistence(from what I've been told).
A polymer finish will run about the same as BC.
Check in with Cogan Custom/Accurate Plating&Weaponry, Ford's Guns, Checkmate, and possibly Birdsong. They'll know best....:wave: