$800 might be an insult. Before you offer anything, ask him what he paid to have it engraved. It will not be worth price of gun + engraving, since it is used, and people usually take a hit for customizing & engraving, but $800 would be a STEAL if the engaving is any kind of quality work. A top end engraver might charge $2000 for full coverage, and that gun seems to have extensive work. It might easily fall outside your price limitations, or your offer might fall out side of the sellers expectations. Either way, if it is a friend, you might want to proceed delicately, or you might insult your friend.