Mark Carpenter could have just printed photorealistic carbon fiber stickers and plopped them on Lego tiles for his kids. That is apparently not his style: these are 1x2 tiles milled from actual carbon fiber. The tiles are a total of 3mm thick.
Carpenter credits a brainstorming session with his Lego-loving children with inspiration for the idea. The tiles are currently being funded through ; with 22 days to go as of this writing, he's gathered $2693 of his $8000 goal. If he reaches the goal, Carpenter will give backers various combinations of 10-packs of tiles. The tiles work out to between $1.40-$2 each, depending on which funding level is selected.
What they'll retail for outside of Kickstarter is anybody's guess, but Legos are expensive, and $1.40/per isn't completely outlandish for the sort of person who would seriously consider buying actual carbon fiber tiles for their project.
I've seen a few really cool Lego car builds lately that would look great with a few of these attached in key places.