I think its definitely cheaper to buy one done. BUT like John said, when you build them from the ground up, you know EVERY SINGLE nut/bolt/wire etc. You put it together exactly how you want it done. And you dont have to worry about buying someones pieced together problem. I am in no way saying that you will get a problem car, but you always take that chance. If I was buying a put together car, I would try to buy one with little mods. If it is highly modded, it has probably been driven hard and then you have to worry about torn torque boxes,twisted subframes etc. There are definitely pros and cons to either situation.