When the primary driving point is "Cheapest" you usually get what you paid for. It's been years since I built from kits but seldom did I not have to replace some part or materials. One has to have some common sense. If a wing spar in the kit for a 5-7 Lb plane is 1/8" liteply something should tell you that it would be better to use a piece of aircraft birch ply or some type of reinforcement added. One kit I bought had a piece of hard balsa for the stabilzer that was so heavy I would have had to put a brick in the nose to balance the plane. I just substituted some of my balsa on hand.