Macys has the Nike Men's Brasilia XL Training Backpack (several colors) for $28. Shipping is free when pad your order with a $3 beauty item. Otherwise, shipping adds $10.95. It features a padded, adjustable shoulder straps and multiple interior and exterior pockets/compartments. It measures 19"H x 13"W x 9"D.
Amazon has the John Deere Boys' Toddler Backpack, Yellow (JFL742YT) for $11 with free shipping on $25+ or with Prime. List price: $20. Features reflective tape, name tag inside and plenty of room for school supplies.
Has good Amazon Reviews.