I saw a vendor selling stencils for $50, but I assumed they were steel. Steel stencils are the only ones I've ever seen. So possibly they were mylar or something else. Seems expensive for mylar though. Is that what non-steel stencils are made of?
They can make them out of a nylon screen sort of like a silk screen for t-shirt printing. That type needs a wood or metal frame and the screen with the stencil you want to use is stretched and attached to the frame. You either manually align the screen and board or use a machine that holds the board and screen in alignment