Tomtop offers the Free Knight 50-liter Outdoor Sport Backpack in Green or Grey for $19.99. Coupon code "50LOFF5" cuts it to $14.99 with free shipping. That's the lowest price we could find by $10. It features water resistant and tear resistant nylon, S-shape ergonomic padded shoulder straps, padded back support, adjustable chest belt, and adjustable waist belt.