As a reader discovered, Amazon offers Prime members the Akai Professional Project 50X Over-Ear Studio Monitor Headphones in Black for $18.71 with free shipping. That's the lowest price we could find by about $7, although we saw them for a buck less in August. These closed-back headphones feature a 50mm dynamic transducer, 10Hz to 30kHz frequency response, collapsible design, swiveling ear cups, straight and coiled 6-foot detachable cables, 1/8"-to-1/4" adapter, and leatherette travel pouch.

Update: Clip the 15% off coupon on the product page to drop it to $15.90.