Ruger didn't ship any Single-Sixes with the brass g/f installed to my knowledge. But,,, they can be added easily enough.
Pull the grips off & check for factory markings,,, MR3-DB and if so,,, figure in at least $250 for the g/f in good shape. If it has the wide Super trigger,,, even better. But,,, deduct the cost of a replacement correct g/f & trigger.
If it's an aftermarket g/f,,, then figure $150-$200 for one of those.