Sony Noise Isolating In-Ear Headphones for $15 + free shipping
GeekDeal via eBay offers the Sony Noise Isolating In-Ear Headphones in Blue, model no. MDR-EX210B, for $14.95 with free shipping. That's the lowest total price we could find by $5. They feature 13.5mm drivers, three earbud sizes, and frequency response of 5Hz to 24kHz.
2 very similar deals were also reported by some other sources: