Walmart offers the refurbished Acer 28" 2160p 4K LED-Backlit LCD Ultra HD Monitor in Black, model no. B286HK, for $294 with free shipping. That's $86 under our mention of a new unit from last winter and the lowest total price we've seen for this monitor in any condition. (It's $155 under the best price we could find for a new model today.) It features a 3840x2160 native resolution, LED backlight, and HDMI, Display Port, and DVI inputs.

A 90-day warranty applies, but it's unclear who backs it.