The shop will most likely cut out that piece and put in a new piece of metal especially considering it looks like the rust is in there fairly deep. Sanding down/bondo would prob not be worth it for rust that looks this deep. Prob a $700-1000 job, depends on the shop and the quality job they provide. Up to you if you feel it's worth it to repair the car.

There's a reason car washes should be done frequently in the winter in rust belt states, salt absolutely destroys cars.

 

Probably got hit there at some point

 

Hasn’t been hit there that I know of.

If a shop will cut out and replace it Nd paint it for under 1000 I’d think it’s worth it. I’m going to start calling around.

 

it looks the rust was painted over and now it's just rusting through entirely now, but that's just a guess. The spot right where the side skirt meets the rear fender always gets hit with rust for me even when I got it sanded down and repainted

 

Pictures like that are why I don't drive my IS350 in the winter lol

That's going to be an expensive repair especially if you want it un-noticeable. If you like the car enough then go ahead and fix it.. if not I'd ride it out and save your money for something new.

Whats the other side like? the same? Its tough to say exactly how much it will cost for repair, as mentioned above each shop will price differently and some will have better quality finishing then others.

 

 

I feel like you could DIY this if you really wanted to. I doubt it's going to be perfect but It'll be much better then what it looks like right now. Maybe you could grab the color code in a spray bottle and do it yourself.