A whole new rear sight assembly is going to be about $50 to $60 and is very easy to install.

Replacing the blade is about $10 to $15 but requires more work and special screwdriver bits. There are videos out there that show you have to replace the blade. I think just about any S&S revolver from the last 50 years or more is going to be the same basic procedure to replace the blade. It's not hard to do but I'd watch a video or 2 and determine if it's something you want to mess with before deciding.