That form of decoration is not called "engraving" it is "scrimshaw".
Started as a picture scratched in bone then inked . Now it is also done in plastic.
yes, the cost ( added value?) would be in just who you have to do the scrimshaw, we used to set up at the shows years ago, down the row from woman named Sara Brady , from the OGCA and she did awesome scrimshaw work ...your grips appear to be on the longer side, so may be for an S-47 frame......... $45-50 polymer grips, with the one panel scrimshaw, so add some to the price..............
and yes they look nice.....