These days, I might have some doubts that the $1500 repaint bill would include welding in new metal. My bet is the new patch is going to be glued in place.

You should cut out the rust, treat the metal with a rust converter (for the rust you missed cutting out), form a patch and glue the patch panel over top of the hole surrounded by the good metal, then add filler to the edges to make it smooth, and paint it.

Anything short of cutting out the old rusty metal and replacing it with new metal will guarantee the rust will return, possibly as soon as 6 months.

Once you do it yourself, and find out just how hard it really is, I'd bet the next time, that $1500 won't look so bad. Gene