Walmart offers the Wintec Filemate Plus Series Backpack in Black/Grey for $12.35. Opt for in-store pickup to dodge the $4.97 shipping charge. That's the lowest price we could find by a buck. It features a main zippered compartment, two zippered side compartments, and a laptop/netbook/tablet compartment.
Of note, it's also available in Black/Pink for $16.99.