HELP!! My car is rotting away!!

[RMARIANI]

A little over a month ago, I noticed a rust patch on my driver's side rear quarter panel in the wheel well just above where the rear bumper cover starts. Well, yesterday I took a paint/rust remover wheel and went to work. After I got the top layer of paint and rust off, I started to notice that there was a hole under it. Its hard to describe, but the bare metal was shiny, in one part it was darker. I was thinking it reminded me of a cavity. I went pretty deep into the hole and was still removing black/rusty metal. I don't want to just fill this in with Bondo, as I'm sure it'll just rust through again. What are my alternatives to a body shop?? I didn't plan on painting the car for at least another year, but I don't want her to slowly rot away either.