Walmart offers the Bluestone Bamboo Memory Foam Pillow for $14. Opt for in-store pickup to dodge the $5.97 shipping charge. That's the lowest total price we could find by $6, outside of the mention below. It's hypoallergenic and features a removable, washable cover.

A close price: Target has it for $11.89 $10.70 plus $4 for shipping using code "SUMMER10".