Head-Director via eBay offers the HiFiMan HE-400 Over-Ear Audiophile Headphones for $299 with free shipping. (HiFiMan via Amazon has them for $5 more.) That's the lowest total price we could find by $100. They feature planar magnetic drivers, a 20Hz to 35kHz frequency response, 35 ohm impedance, and 10-foot cable.

Head-Director via eBay also offers the HiFiMan HE-500 Over-Ear Audiophile Headphones for $599 with free shipping. (HiFiMan via Amazon also has them for $5 more.) That's also the best price we could find by $100. They feature planar magnetic drivers, a 15Hz to 50kHz frequency response, 38 ohm impedance, and 10-foot cable.