Presuming that the body is straight and needs no major repairs 1000-1200 would be a fair price. The question becomes what do you do with it: parts for the carbed turbos are not abundant or cheap, and they won't have the power or driveability that the sfi cars do. As a starting point for either a v8 (Buick of course) or later turbo swap it sounds promising, but that's about it.
I respectfully disagree. My engine is stock, it drives very well and I'm running as fast as the SFI cars. I think it would be foolish to pull the turbo V6 out for another motor.
If it's rust free and doesn't need major work, $1200 is a bargin for a performance car.
Rich is definitely a better source on the early models, I don't doubt him. (provided me with a fair amount of info on my 82 GN) I guess the big question is: how much work does this car need? If it runs you'll be fine. But if the engine tossed it's cookies you could be in for a good time.