With orders of $25 or more, Amazon offers the Maybelline Great Lash Washable Volumizing Mascara 0.43-oz. Tube in Very Black for $4.39. Clip the $2 off coupon on the product page to cut that to $2.39. With free shipping, that's around $2 less than you'd expect to pay in local stores. This hypoallergenic formula purportedly doubles lash size.

Note: This item is part of Amazon's "add-on" program and can only be purchased with orders of $25 or more.