Blinq via eBay offers the refurbished Dell 28" 4K LED-Backlit LCD Monitor, model no. P2815Q, for $219.99 with free shipping. That's $79 below yesterday's mention of a new monitor and the lowest total price we've seen for a 28" 4K display. (It's a current low for a refurb by $90.) It features a 3840x2160 native resolution, LED backlight, DisplayPort, mini DisplayPort, and one HDMI input.
Note: A 90-day Blinq warranty applies.