Most of the training facilities I have been through that use some sort of "kill house" do so on the cheap. I have seen them made of railroad ties with old tires in between and I've also seen them made out of simple plywood. Old furniture and such is placed inside and can be moved around and made different each time. Most of us here probably have enough money in our pockets right now to build one. Such a facility is designed to be shot up anyway and needs to be cheap and easy to replace. Put a few picture targets inside and your ready to go. If a wall gets shot up, go to the hardware store and for ten bucks get a new one.