Amazon Coins can be redeemed on eligible products in the Amazon Appstore. Note that promotional coins will expire on the last day of the month one year after they were acquired.
Amazon also offers Prime members the Koss KTXPRO1 Titanium Portable Headphones, model no. 145517, bundled with a $2 MP3 credit for $9.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $5.74.) Assuming you use the credit, that's the lowest price we could find by $8. These headphones feature 15Hz to 25kHz frequency response, foam ear cushions, and cord volume control.
Of note, GO EACH via Amazon offers it in Black or White for $29.46 plus $5.49 for shipping.