Most people are way to rough on their rusty cast iron, imho. I take a scrub pad and rub it down, rinse it off, heat it on the stove and wipe it down with lard. 2 or 3 times of this usually fixes 99% of rusty skillets and dutch ovens I've fixed, except for those with thick scaly rust, in which case I'll start with a hand held wire brush to knock the scale off, then start as above.
Any skillet I've seen that had a wire wheel taken to it was ever right afterwards. Also, I never let any oils or grease that is not animal based touch my skillets, and it makes a huge difference.