Walmart has a lot of backpacks under $10!! You can check them all out at THIS LINK.

A few of the backpacks you can get for that price are these:

Eastsport Front Mesh Backpack (Colors: Black, Carnation Pink, Grey) Was: $9 Now: $8	Eastsport 17.5″ Backpack (Colors: Black, Clear w/Black Trim) Was: $8.88 Now: $8
Eastsport 17.5″ Mesh Dome Backpack Was: $8.88 Now: $8	Eastsport Mesh Bungee 17.5″ Backpack (Colors: Black; English Rose; Navy; Purple) Was: $8.88 Now: $8