You need to get the rear seats up, and look for the head of the bolt that's holding on the rear subframe. Check that general area for metal distortion. You should also check the rear corners of the sill where the subframe support plate bolts on (two bolts through the sill).
If there's serious distortion in the metal, you might as well scrap the car; you'll have bent the back end so badly that you'll never get the geometry back in line. If things are ok there, you'll still need to drop the subframe to repair the trailing arm you've bent, and to assess any damage to the diff mount. You'll then need to cut out part of the boot to weld in a new section, as well as a whole rear quarter panel. Pictures of inside the boot would also help to assess the damage.
Either way, a lot of work to get that back on the road
