$500 is very generous. I'd wait a month then offer $300. He isn't going to find a nut like me, or you, to buy it. I recently bought my third GV 250, a running bike with bald tires, 7700 miles, cosmetic issues, for $800.
Here in CA the back registration fees/penalties are horrendous if it's not kept current. People let them sit in the garage and neglect to pay the plate fee or non-op them to avoid penalties.