MacMall offers the Case Logic 16" Checkpoint Friendly Laptop Backpack, model no. ZLBS-216BLACK, for $17.99 plus $7.96 for shipping. Outside of the mention below, that's the lowest total price we could find by $7, although several stores charge around $45. It's designed to accommodate laptops up to 16" and features a bottom grab handle, luggage strap, and document compartment.

A close price: Newegg has it for $27.99 after coupon code "EMCPEHW93". With free shipping, that's another low.