They really aren't that cheap when you factor in the cost of the sideskirts, molding them in (if you do), and painting to match. If they are molded in, it's probably gonna take painting the whole car to make it look good, because you will have to paint part of the body of the car as well.
I honestly thing the sides could get away with not being molded, but the rears have that ugly seem line that needs molding in if you ask me.