CocoPark800 via eBay offers this Unisex Galaxy Canvas Backpack
in four colors (Blue pictured) for $7.89
plus 59 cents
for shipping. Outside of other eBay sellers, that's the lowest total price we could find by $3, although we saw it for a buck less last week. It features two main compartments, adjustable shoulder straps, and double side pockets.
Note that this item is estimated to arrive in two to three weeks.