You could buy a mig welder (with gas), read some tutorials on line, ask questions here, practice on some scraps, and then weld a patch in yourself. I took that approach and welded a new spare tire well into the trunk of my car and now the rust is fixed for good. Then when I painted the engine compartment I welded some holes shut and butt welded in a patch by the battery. It takes some time to learn but the average guy can do it.