REI offers the Seattle Sports Supstow Hip Pack & Leash for $14.73. Choose in-store pickup to avoid the $5.99 shipping fee. Outside of the deal below, that's the lowest price we could find by $3, although we saw it for $3 less in May. It features a zipper closure and board tether.

Note: It's not waterproof. A close price, offers it for $8.86 plus $5.99 for shipping.