At the Disney Store, receive free shipping
on your entire order with purchase of any back to school item
via coupon code "SCHOOLSHIP". (The cheapest item is the lunch box
.) That ties a similar mention from two weeks ago as one of the best such shipping offers we've seen from this merchant. Sales tax is added where applicable.
A best bet is this Personalized Glittering Disney Princess Backpack (pictured) for $12. With free shipping via coupon code "SCHOOLSHIP", that's $13 off and the lowest total price we could find.