Just remember the pawn shop rule - they likely have half of their listed price invested so dicker away and do not be afraid to walk. IMO that is a $400 gun without the factory grips.
Having worked in a pawn shop for several years ( part time ) they are most likely in a 1/3 the asking price or even 1/4. Pawn shops are notorious for offers way less than actual value and asking full top dollar. I would offer away, worse he can say is " NO "