REI Garage offers the Sea to Summit Solution Gear Trip Cockpit Cover and Bag in Blue/Black for $17.73. Opt for in-store pickup to dodge the $5.99 shipping fee. That's the lowest price we could find by $18. It features an adjustable shockcord, mesh sides, and large curved zip.

Note: REI members can take an extra 20% off this item via coupon code "MEMPERKS". A lifetime membership costs $20. (You can sign up at checkout.)