Luckily, we are beyond the typical back to school scenario, mearly replacing items as needed, tending to reuse what we already have. This blog post came into my feed this morning: http://www.cheapism.com/blog/cheap-backpacks-for-school-14202/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+CheapismBlog+%28Cheapism+Blog%29#up-next
Frankly, I find the approach to be penny wise, yet pound foolish. A $20 backpack will not offer the same mileage as a more expensive one, often needing replacemnt within the same school year. Additionally, a character image one or one that is too feminine/masculine can not be passed on to another sibling as popular character's change (have you noted how much Else and Frozen stuff is out there now?), and few boys want a clearly girl themed back pack.
Instead, my approach has been to buy generic colored, solid colored backpacks from one of 2 companies that stand behind their product with full replacement: Jansport and L L Bean. For $30-$50, I have a back pack that will go thru several siblings before I try to resell it, either at a consignment shop or thru a private sale. Makes more sense to me.