those arent 18s
^^ What they said. It is indeed off a Bonneville, and they are 17s. The only stock 18s on a Bonneville were the GXP wheels.
http://www.autopartsfair.com/pontia...le-2005-oem_alloy_wheel_rims-aly06549u85.html
As to value, unfortunately, they are not one of the more desirable wheels, so they won't be worth much. Someone may pick them up for winter beaters, or a cheap upgrade in size/style for a GM that came with even less desirable wheels. If he could get $200-$250 for the set, I'd take it and run.