Rusty boi

Heyo,
So I bought a 2005 mustang gt a few months back, and I recently noticed a large amount of rust bubbles on the bottom of both rear quarter panels. I'm not sure I want to know this, but how much will it cost me approximately to fix? It a patch on both sides that is about 2x6 inches large, on the very bottom and frontmost side of my right rear quarter panels(right above my side skirt) Thanks ma dudes