FasterSale via eBay offers this Waterproof Pouch with Armband Strap for iPhone 4, 4S, and 5 for $3.39 with free shipping. That's a buck under our August mention of an almost identical pouch and the lowest total price we could find for a similar one now by a buck. It's water-, dust-, dirt-, and sand-resistant and features an adjustable armband.

Note that this item ships from Hong Kong and could take up to three weeks to arrive.