Bed sides rusting

[Sesco4]

I know our trucks are infamous for the rear fenders rusting and mine is starting to rust around the lip of the fender. I took it to a local body shop and they said a cheap fix would only last six months to a year before it comes back. On the other hand if I fix it right and replace the bed sides the cost is through the roof so I'm just wanting some ideas and suggestions on what some of you with this issue have done.

[powerstrokeFD16]

you can get a southern bed with no rust for $1200.