Hi Bob
Best of luck with the sale. They do occassionally appear on ebay, so a search of completed listings may be worthwhile research, but I think that there are a couple of problems here.
Anyone who wants a finished model wouldnt be interested in part finished, and any one who wants to build his own wouldn't be interested in part finished, as he wants to do the building himself; the exception being if its very cheap!
In my experience part finished models of any type are, unfortunately, of very little value, I feel his best bet is to get it finished. Even then it would need to be a super model to have any real value; or go the other way and sell the parts. Either way the value will probably be much less than the cost of building.
Ask anyone who's into kitcars and you'll find out that they have to be exceptional to command good prices, and half finished ones just don't get the money.
There was a DBR tractor kit on ebay, some months back, complete kit, with extra motor, speed control, and other bits and pieces including a completed body tub, all sold for about ?400, probably a third of cost!
Perhaps some detail pictures posted here will generate some interest!
Best of luck
regards
Walter