Prime members only. Amazon has single QuestBar Protein Bars, bundled with a $2 credit toward additional protein bars, for $2 each.

There are currently around 15 flavors available to order as single bars (select flavors under "26 Flavors" and look for "Try it for $2.00"), and you can order one per flavor, making it $30 shipped for 15 bars plus a $30 credit.