Newegg offers the refurbished Asus 28" 4K Ultra HD LED-Backlit LCD Monitor, model no. PB287Q, for $359.99 with free shipping. That's $27 under our mention of a new one from four days ago and the lowest total price we've seen for this display. (It's also $27 below the best deal we could find for a new one today.) It features a 3840x2160 (2160p) native resolution, LED backlight, speakers, and DisplayPort and two HDMI inputs.
A 455-day warranty is provided, although it is unclear who backs it.