I bought a set of the factory flares for a pickup at the local Pick-n-Pull for $40, screwed 'em on my 4-door. The fronts fit just as they should, but the back flares (obviously) covered both the door and the fender.
So I took a RotoZip tool, and followed the contour of the rear door, cutting the rear flares into two-piece units. The flare DOES overhang the door on the bottom, it doesn't conform to the rocker panel like the "true" 4-door flares. But Big Deal....