A lot of it is location,location,location,just like real estate..
Haul that Firebird here and you'd get 15K for it probably,because there IS none up here,the few that might be, are either rotted junk,a hacked up one with non original drivetrain,or someones pristine 30K original owner type car..
A Nova like that here would bring 5 or 6 grand at a swap meet for a "project car",I have seen much worse sell for that here,in peices,like an erector set!..
In CA and other states where these kinds of cars didn't all rot away 20 years ago and junkyards crushed the rest,I'm sure prices are more reasonable..hell,even a air cooled VW here is dam hard to find for less than 3 grand that hasn't been all patched together..out there there is probably thousands to choose from...you look on craigslist for one here,you'll see maybe ten for sale in all of new england,and 90% of them are rotted or patched up junkers..the ones that are not,go for 6-10 grand..