Hard to say.
For comparison, a buddy just sold a '04 G3 1860 sc w/ '05 90 Yam 4st ( hrs unknown, probably around 350-500), good trailer, 55 lb MK foot troll. motor. Boat was in great shape, not beat up at all. Trolling plate, trolling rod racks, 2 GPS fisfinders inc. $7500.
You're looking at a bigger rig, no hrs on the motor. If its not beat up, hours check out ( may not be able to?) and compression is good, it's probably not that far off. New rig like that is low 20k's I bet.
I'd offer something less than that, in a respectful way, and go from there. If its something you want, you can come up to meet him. The market is not saturated with rigs like that, as you already have found out.