For insurance purposes I would add up the cost of all of the parts and pieces in the original kit, and then triple that. If you ever watch the Antiques Roadshow you'll see that when they give auction estimates they'll sometimes also give an insurance estimate and usually the insurance estimate is almost twice as much as the top auction estimate.
I say to triple it because of the extra expense of having everything assembled and painted. If all the pieces cost $1,000 it's realistic to expect that that kit fully built and ready to run by an experienced RC modeler will be about three times the cost of the components.