BAS sells pre-cut kits of 2 varieties - the older style, thicker 40mil stuff runs 39.95, new style, thinner stronger 23mil variety runs 49.95 (BAS prices from memory here).
While looking into other, less expensive options, someone posted here regarding uncut sheets of 40mil headlight protective film from chasetechno.com. This is the older style film that comes in 13.5x11" sheets for $15US. As it happened, the poster of that original message was so closely affiliated with the company that his email address was listed on the "Info" page for the company - not exactly an unsolicited opinion, and I got no others about the company or the specific product.
Griot's Garage, an otherwise heinously expensive establishment (www.griotsgarage.com), carries the 23mil newer variety of film in a 10x16" sheet for $22US. Pretty reasonable, especially considering the source. The Griots product also comes with a spray for your lights to help in positioning the chunks you cut, so you don't have to get it exactly right the first time.
I went with the Griot's product. There is a bit more company behind it than the Chase product, and I will now be on their mailing list so I will be able to see all the cool, overpriced products in the catalog for the next year or two. The entertainment will probably be worth the $7 differential. The thinner film will also not be as visible on the lamps.