How long has the car been in Guam. When I was there you could put your hands through cars after a couple years. I remember seeing pictures of your car and it is nice in the pictures. However, I would agree that about $3k would be the neighborhood. If it had the newer M50 motor maybe $5 - $7k depending on year.
Since you can't really drive very fast on Guam (except on the back road to Anderson), It would seem to be a pretty good car for there. Except for when it breaks and then there is no one to fix it. Better to stay with something Atkins-Kroll can repair.
Mike
Mike Holbrook
Meridian, Idaho
1992 535im, 17", Euro M5 Throwing Stars 8's & 9's, FK-451 235/45s & 255/40s, M5 Sway Bars 25/20, Conforti chip, Lowes Ram Air, glass sunroof