How to buy a 68 Cuda.

Lower rear quarters, trunk extensions, rockers just in front of the rear wheel wells, front frame rails where they kick up to meet the front suspension, torsion bar crossmember where the hex sockets are welded, front floors. All these areas need to be checked out for rust.
Front and rear bumpers are the same for 67-69 cudas, not hard to find, and they're reproduced. Grille and especially deck trim are important as all 3 years are different. New tail lights are available but it's not like buying just the lenses gor a Duster. Repop sheet metal is available but the full quarters are fastback only. Full skins also available. Check AMD web site (for one)
As a driver it's fine as is. Show car, not there yet. Depends what your plans are. Notches are less valuable than fastbacks. Expect mud in lowers quarters, more likely than not.
If it's fairly solid, I'd say 5k.