Ummmm, that's pretty - make that very - thin and not terribly rigid. If you're doing curved shapes like gun tubs or something it should be OK, but for wide, flat expanses I'd go with something thicker. That said:
http://www.evergreenscalemodels.com/Sheets.htm#White%20Economy%20Packs - 3 6x12-inch sheets are listed for $2.99 retail. Any reputable hobby shop should stock Evergreen products.