You need to consider usage patterns as you evaluate the cost/quality value curve, though. $35 for a Jansport for a school kid who will brutalize their pack regardless is probably a much better value than a $130 Osprey that is objectively superior but which a teenager would still brutalize to death in 1-2 years of daily school use.

Fwiw, my elementary kid is on year 3 with her Lands End pack (which is way crappier than the Lands End / Eddie Bauer / LL Bean school packs from the 80s-00s), and my two older kids use Osprey Nebula packs in high school -- both also on year three. The Osprey packs are terrific, but would be overkill for a younger kid, and we purchased them mostly because our kids bike to school and needed something that would comfortable carry 20+ lbs of crap.