LightInTheBox offers this 15.6" Laptop Backpack in several colors (Pool pictured) for $15.99. Coupon code "LITBPC" cuts it to $8.99. With $9.90 for shipping, that's $13 off list and the lowest price we could find. It's made of Oxford cloth and accommodates up to a 15" laptop.

Note: This item ships from China and may take two to five weeks to arrive. Uncheck "Add Shipping Insurance to your order" during checkout to remove the 49-cent fee.