I had a local jeweler do one of my SBR lowers based on the recommendation of a well known ARFcommer and fellow C3 nut, and he totally screwed it up. Since then, I have stuck with folks who specialize in NFA engraving and know the game, even though it takes more time and $$. I have not been disappointed.
If you do go the trophy shop route, make sure they are capable of meeting the ATF's requirements for size and depth and are cool with working on firearms.
Ray Saltzman of Saltzman Gun Works, Inc. does it for around $25 or $30. He's in Tipton. If that's too much of a drive, Elmore's will handle it. They're in Greenwood. Elmore's actually sends the lowers to Ray Saltzman or at least they did a couple of years ago.
Ray has done a couple of my lowers. The lettering was of proper depth and size. It was even and straight.