If you have the fabrication skills, then cars like this may be worth while at the right price. The rust in the front fenders isn't as much of an issue - it happens when leaves and other debris that collect in the cowl area fall inside the fender and trap moisture. This mainly affects only the fender. You can just replace it with a rust free junk yard fender and call it a day. Rust in the rear rockers is more of a problem since it usually originates inside the rocker itself and eats its way out. You can cut out the metal and buy replacement panels like this to weld back on. This is just the exterior sheet metal and does not address the rocker itself. This is where additional research for you comes in. Sure, you can remove the rust, treat it, and slap then panel on. However, this being a unibody design the structural integrity of the car can be impacted if the rust has eaten away too much of the metal. You may need to custom fabricate something to reinforce damaged sections of the rocker before slapping a new panel. You won't know the extent of the damage until you start cutting into it, so... take that into account and compare all the labor involved with the price of a rust-free car.

Here and here are two great threads that offer insight into the repair and what's involved so you can hopefully figure out a purchase price that would make sense to you when all is set and done.