If the floorboards are intact and there's not any mold or mildew in the interior, I'd offer $850.
If the floorboards are rusted through anywhere or it has mold or mildew in the interior, I'd offer $200-300 at the most. Fixing those problems would almost require a parts car, or that car would be a parts donor for another II if either of those problems were present. (just my opinion, I've seen far worse cars restored, I just wouldn't take the time or invest the money right now myself.)
__________________ 1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".) | 
1977 cobra, would you buy it? 
