CPO Outlets via eBay offers the DEWALT 1/2" 20-volt Cordless Impact Wrench (bare tool, no battery), model no. DCF889B, for $129 with free shipping. That's the lowest total price we could find by $20. It delivers up to 300 foot-pounds of torque, 1,500 rpm, 2,300 IPM, and more. It requires a DEWALT 20-volt battery, sold separately.
CPO Outles via eBay offers the Milwaukee M18 18-volt Lithium-Ion Cordless Impact Wrench, model no. 2651-22, for $249 with free shipping. That's the lowest total price we could find by $50. It features a 4-pole frameless motor, 3/8" friction ring, built-in LED light, and two lithium-ion batteries.