Altatac via eBay offers the High Sierra Wave 70 Lightweight 2-Liter Hydration Backpack in Royal Blue (pictured), True Navy, or Black for $14.99 with free shipping. That's tied with our Black Friday mention as the lowest total price we've seen. (It's also a current low by $5.) It features a 2-liter bladder, mesh straps, and zippered front accessory compartment.