Ask the company that makes the gun. All arms companies either have in house engravers or have ones they deal with regularly. This will not necessarily give you a low price, but you could get better work than going on your own.
If you just want initials, any jewelry shop can do it or have it done, and there is a list of engravers in the back of the Gun Digest. Some advertise in Shotgun News, also.
Jim
