Colt offers several levels of engraving - from about 1/4 of the weapon to full, complete coverage.
Contact the Custom Shop directly for pricing and you can talk to one of the engravers about what you want, since prices change and brochures don't always keep up.
No idea what the cost might be, though I've heard it's competitive, but since it'll be 'factory' engraving done by a Colt engraver - the added value will enhance your weapon.
What you want done is pretty simple, and should prove no problem.
Now - that's 'your' weapon, and your engraving ideas may or may not appeal to another's taste if you decide on 'really' personalizing the piece, whereas the standard styles seem to always appeal.
That part is up to you, and buffing off and re-bluing the engraving on the backstrap's also a simple affair, as well.
Vaya,
Scouts Out!