Shreck, I'd think, depending on the condition of the lock, about $150/$250 for a rifle size lock. And maybe a bit less for a pistol size lock.
I have a round faced pistol lock, stamped T. KETLAND in block letters, on the Inside of the lock plate. It has vine engraving behind and ahead of the hammer, no bridle on the frizzen or on the tumbler. It works great, still sparks nicely, is a silver color with a little bit of rust. I bought it with most of a brass barreled pistol for $300 back when prices were high.
John