I would think a semi complete no interior FGF shell would go around $1000-$1500 without running gear, but it should be in decent shape, maybe need a hood, fender, valance, or maybe a quarter skin and trunk pan or combination of some of those. But not all of those. A good body should bring over $2000.
The car in that picture to me is a $800-$1000 shell. If it had fenders and usable front bumper parts, or had been media blasted, maybe $1500, not $2800. That's a redicules price to start a project like this with.

Repo body parts alone will run into the thousands. Why buy a rusty hulk when I can buy a running car, part it out and possibly sell the good stuff to someone building one of these rusty hulks. I'd save thousands on body panels and body work.
But just thinking out loud, I have no intentions at this time to part out a running car, for now anyway.

The only way I see it as these prices being a non issue is the fact that in the end, paying $1000 more for a shell than it's worth is peanuts in the grand scheme of total restoration cost.
Maybe that's the problem. But I'm not restoring this car, I'm building a race car, therefore I can't pay what some would consider a restorers fair market value for a shell. Nor can I justify buying a car that needs doors, fenders, full quarters and floors, those are the most expensive and time consuming body parts to replace. If I get a car that needs all that, it needs to be cheap as the only valuable part is the front subframe and roof.