First of all, yes, we are serious. This entire costume - the dress, at least - can be made for about a buck. And that dollar is the cost of the red fabric. Other than that, all you need is a little needle and thread and you're good to go.
If you're handy with the needle and are in need of a last minute Halloween costume, check out this video to learn how to whip a Little Red Riding Hood costume up cheap.