Marc has bought A4 sheets at 57 CHF sheet, however [http://www.aliexpress.com/item/Scentless-laser-rubber-sheet-for-stampEco-friendly-laser-rubber-sheet-for-stamp/815226364.html here] you can get them for 20$ per single sheet, or for 7$ [http://www.aliexpress.com/item/Scentless-laser-rubber-sheet-for-stampEco-friendly-laser-rubber-sheet-for-stamp/815226364.html here] if you buy in lots of 5.
=== Mylar/thin plastic ===
[http://juanjchong.com/2014/cutting-mylar-solder-stencils-from-expresspcb-and-eaglecad-files/ This] might be an interesting technique to try for thin plastics, such as those used for PCB stencils. The idea is that you have two layers of the material that you cut at the same time, the top one will be scrapped after, but the bottom one should be good - need to try this technique.
=== Others ===