EagleWill via eBay offers this Military-Style 3-Liter Hydration Pack
in Black for $13.99
with free shipping
. That's $6 under the best price we could find for a similar item sold elsewhere. Features include 600D high-density waterproof Oxford fabric, adjustable shoulder straps, a chest belt, bite valve, and neoprene tube.
Note that it's available in three other colors for 60 cents more.