Doug, a quick check on current market pricing can be had on eBay and the other, usual web-based suspects for selling LBCs. BGTs haven't been fetching big premiums lately, but are in my opinion are maybe the best value out there on any LBC.
Without any info or photos of your BGT, I'd say a good sale price might be anywhere from $3,000 to $6,000, IF the car is in good nick mechanically and cosmetically (besides the paint) and doesn't have any significant rust anywhere. $6,000 would be tops if the paint's really bad but the rest of the car is in very good shape.
That's just a wild stab, what I'd pay for a nice BGT that only needs a paint job.
Post the car here, and on eBay where you can't lose by setting a reasonable reserve.