I use stencils that are machine cut and can be used over and over again. They cost anywhere from $60 to $100. What you can do for your one time application is to make your own out of stiff cardboard. I've done this and it will work. Cut a piece of stiff cardboard. Draw, trace, whatever, your design. Then cut it with those sharp hobby knives. Make the cuts as perfect as you can. If your LINE-X dealer is not familiar with how to use your stencil, let me know, and I'll explain it to him.
Here's one, Army Airborne:
