The subframe also looks like it took a major hit underneath the car (enough to bend it all up, and its made of stamped steel). Unbolt the subframe and check the metal where it bolts to the frame. If its hit hard enough the attachment points in the frame may bend or tear, or the entire floor board may be rippled/creased. If this is the case, the frame is pretty much unrepairable (will cost more to repair than a new frame). Also check the entire undercarriage of the car, whatever hit the subrame could have destroyed other parts of the frame underneath. If you didn't have a connection to a body shop, I'd say scrap it, but otherwise you might be able to have it repaired at a economical price (if the underbody isn't bent to ****). Welding in new frame rails is NOT an easy thing to do. Only someone with massive welding experience should attempt this, and even so, it will be VERY difficult to get it aligned properly (the body shop should be experienced in frame restoration, and have access to a laser frame machine to see if the rail is straight).

 

Looks like a cool project if you can do it yourself.
However, personally I’d just part the car. After all the rebuilding process you’re still going to have a salvage title car.