Amazon offers the Velcro Sticky Back 18" x 3/4" Tape in Clear for $2.97. Plus, Amazon Prime members bag free shipping. That's the lowest price we could find by a buck, outside of the mention below. This hook-and-loop fastener purports to adhere to most surfaces.

A close price: Home Depot charges a few cents more with in-store pickup.

Update: It's expected to ship in one to two months.