Mieiel6792014 via eBay offers this Tactical Travel Backpack
in six colors for $12.85
for shipping. Excluding other eBay sellers, that's the lowest total price we could find by $2. It measures approximately 14" x 7" x 6" and features a zip-closure main compartment, mesh accessory pocket, front zip pocket, padded adjustable shoulder strap, mesh backing, drag handle, and drainage grommets.
Note that this item ships from outside the US and is estimated to arrive within two to four weeks.