Since the frame appears to be 2 rails that should be level, I think you can fix it yourself. Measure to find out which rail is bent & where it is bent at.....usually one rail will be pushed up & if your doors are working okay it will be probably be bent at the firewall area.
If the bend is confined to one area you can cut a pie shaped of the frame & push the rail in place, weld & box.
This sounds easy but, it will take many hours of leveling & measuring first. If the frame is bent over a large area this area will have to be cut out & replaced.
let us know where the damage is BEFORE proceeding