First be real careful about come to you body work, in order to repair rust thru the metal needs to be cut out and a patch panel welded in than the surrounding areas treated and obviously plastic, prime and painting. A guy working out of the back of his truck probably cannot do this job correctly and please don't just let someone just bondo it up.
The cost of aftermarket fenders are about 270 each new and whether you replace or repair you will have to paint. Finally the job itself is not hard but is time consuming and can be frustrating if you have never done body work.
Hope this info helps, I own a paint and body shop as well as a Rhino Lining dealership, glad to offer advice.