Installed implants and artificial body parts doesn't affects colonist price.
Sources: https://github.com/NightKosh/ZeroCostImplants
P.S. As far as implants (and especially brain implants) should become more common for your pawns, I'd like to recommend you to take a look on this mod: https://steamcommunity.com/sharedfiles/filedetails/?id=2227796764
