With orders of $25 or more, Amazon offers Prime members a selection of Trailmaker backpacks from $3.43 with free shipping. (Non-members can spend $49 to qualify for free shipping.) That's the lowest price we could find in any style by $7, although most merchants charge $20 or more for Trailmaker backpacks.

Note that many of these items are part of Amazon's "add-on program" and can only be purchased with orders of $25 or more.