Air body saw is very useful for sheet metal and plastic. They're used in body shops a lot. We use them at work for cutting weird holes in electrical boxes in the panel shop. I use mine at home for all kinds of things. They're generally pretty cheap to buy, and the blades aren't expensive either and easy to find. Sawzall blades will not fit, and for the price of actual blades, not really worth making your own, unless you're in a pinch and need it now.