Mine was less than I thought. I used rubbing and polishing compound and it's looking good now.

 

There is a rule of thumb that what rust you can see is 1/10th of the rust that is there. So while you can polish off the rust that has bled thru on top of the paint, there is more rust underneath the paint.

The correct fix is to sand it down, treat all the rust (Locktite Extends), prime and paint. If it is just on the lip and hasn't grown into the outside of the fender, you can probably get away with touch up paint. If you wait, the rust will continue to spread on to the outside of the fender and then you're into a much more expensive repair and significant loss of resale value.

I'd also be using a mirror and checking the backside of the lip. It seems logical that the salt would sit there and there is a lot more rust there.

 

Ya there was one tiny spot on the top of the lip - under the fender. I sanded and used a Por 15 equivalent. Touched it up after. The other spots only affected the clear coat which I polished and waxed.