PM 9 used value.

My LGS (actually a pawn shop) has a gently used PM9, all black, night sights, one mag and no box for $500 OTD. I just bought his PM 45 2 weeks ago and love it. That was 6 otd with the extra mag, box and the manual. I can't quite justify 5 bills for the PM9, maybe it's a good price. Some opinions would be appreciated. Thanks.