H. H. Gregg offers the Seiki 42" 4K 2160p LED-Backlit LCD Ultra HD Television, model no. SE42UM, for $298 with free shipping. That's $202 off and the lowest total price we could find. It features a native resolution of 3840x2160 (four times that of 1080p TVs), LED backlight, USB, and three HDMI inputs.
Newegg via eBay cuts up to 60% off a selection of HDTVs, monitors, speakers, laptops, and more during its Tech Sale. (The banner states up to 40% off, but we found larger discounts; prices are as marked.) Plus, all items receive free shipping. A couple of best bets: