NewEgg.com has the Sennheiser CX300B 3.5mm Connector Canal Headphone (Black) for $22.99 - $15 rebate (Exp 07/31) = $7.99 with Free Shipping. [PriceSearch]

Note: in addition to the usual requirements, rebate form requires you to send in an old pair of headphones (of any brand/type) in any condition (including non-working).