That is not that bad. Looks like it's surface rust. Easy fix at least for me.
Here is what I would do. I would sand away the rust back to visible metal. Then tape off the main body part and the fender lining.
Get a really nice primer that prevents rust. Do a couple coats. Then lightly sand that to get your final coat to stick.
I'm sure you can find a spray can of your cars color at the local auto store. Then also pick up a clear coat.
Wet sand your final clear coat before you put wax on. Then I would check all other fender wells for rust in that area. If no rust is present wax them up good before winter.
