The pic link did not work for me.
You cannot evaluate the value rationally based on restoration cost. If we did that nothing would get restored. It costs the same to restore a T code as it does a K code for 95% of the work.
People like undiscovered, unmolested projects. And they pay for them if they have good owner history and documents.
Any complete K code fastback that is not a rust bucket with the proper components will be worth $15,000-$23,000.
Lots of people have money for a project car. Plus they get to do it their way. that is why you scratch your head sometimes at the prices paid.
Finished car, especially those that were restored serveral years ago are COMING DOWN in value. The market is weak.
This comes from buying and selling classics everyday all day. Not from arms length observation of eBay.