Sure, you could use plastic stencil material...and I love Cricut stencil material...it cuts very well. But what about using a file folder or regular ol' cardstock?? Yes, these make great stencils, too, and are actually my favorite way to make a stencil.
I'm in the process right now of cutting LOADS of stencils from the Cricut Paper Lace cartridge. If you have a Gypsy or Design Studio or are familiar with the Cricut Craft Room, you can weld images to make your own lacy papers for stencils. Use FIT TO PAGE so your stencil will the the largest theat your machine will cut and see what you can come up with.
To give your stencils a longer life, spray with a few coats of sealer on both sides.