Expensive if it is a reproduction restoration. If it is truly done right, has original panels, driveline and parts it would be hard to duplicate yet still expensive. I see a lot of incorrect cheap aftermarket parts in the bay
Torque boxes, frame rails, floor pans and cowl are particular areas of concern on unibody Mustangs.
I can help you if interested. Appraisals, evaluations, parts, restorations etc is what I do.
