The Crocs clearance page has a buy one, get one free offer that includes 39 pairs of flip flops, sandals, and the classic Croc shoe style. Prices range from $5 to $50 so you'll save the most if you buy two similarly-priced pairs.
You pay for the more expensive pair. Sizes are limited. I like this black and blue Patra sandal for $30 (orig. $40). Perhaps you have a friend who wants to buy a pair with you?