Campus111 via eBay offers the Eaglewill 20-Liter Hydration-Compatible Backpack in Black or Green for $9.99 with free shipping. That's $4 under last month's mention and the lowest price we've seen. (It's the best deal now by $10.) This water-resistant backpack accommodates hydration bladders up to two liters (sold separately) and features a large main compartment, two front pockets, bottom mesh bag, and adjustable padded shoulder and chest straps.