A friend of mine bought a 65 Fastback for $7000. It needed paint & interior. But all the sheet metal was good. I changed the color from black to white, added the Leman's stripes & GT lower stripes. He did all the interior. It took 1st place in a local car show. Very nice car! Go for it!
Just make sure all the numbers match. That's where you can get into a mess. When door panel numbers don't match the front inner fender numbers. And the engine ID doesn't match the car or year. You can see the car at the link below. http://web.infoave.net/~ronniek
Click on "1st Place Car"
66 Coupe, 302, Auto, 3.25 gears. Candyapple Red with White Pearl Stripes. Cragars.
If it's only options were V8 and auto trans it may be a bit high, even with a solid body and no accident damage. How ever, if it has a decentpaint job or interior or a bunch of desireable options like factory 4bbl, handling suspension, a/c, rally pac, deluxe interior, then it'll be worth it.
Beware of rust. It's hard to spot all of it but fastbacks are prone to rust around the rear window and in the trunk. From inside the trunk look up under the rearwindow ledge to see how much rust exists. Also examine the structural supports around the trap door especially near the floor and towards the top.
Hoe complete is the fold down area? No missing panels or panels woth speaker holes in them? The trap door is goingupwards around $100. How is the rear window? I've heard they're around $300 if you can find one.
And check for the usual cowl, lower front door corner, behind the rear wheel well opening and front floor pan rust.