Champion Awards and Trophies in Muncie has done two for me. Reasonable price, good work (mechanical engraving), and he did them both while I waited (two separate occasions).
Sling
Note to add, as I've been warned before:
If the place doing the engraving doesn't possess an FFL, it HAS to be done while you wait as legally they can't have it overnight.
That was the way it was explained to me, if it's not correct, please provide clarification so the info is accurate.