Bill:

I have purchased 3 Berkley Privateer 15 kits on MECA for 35$ each and they were all different sellers on separate occasions. The Privateer 15 is a considerably smaller kit. The fact that it is partially built would be a detriment to me rather than a plus. The glue has dried out over the years, parts could be missing, the builder may not have done a straight and true job etc...

I would say $75 or what ever you feel comfortable giving the seller. Let your conscience be the guide.