Adorama offers the Astell&Kern Beyerdynamic AK T1p Special Edition Semi-Open Over-Ear Headphones for $549.99 with free shipping. That's the lowest price we could find by $649. They feature Tesla drivers, 5Hz to 50kHz frequency response, and 32-ohms impedance. It includes 2.5mm and 3.5mm cables and a 3.5mm to 6.3mm adapter.