Acer via eBay offers the manufacturer-refurbished Acer 28" 4K 2160p LED-Backlit LCD Monitor in Black, model no. XB280HK bprz, for $499.99 with free shipping. That's $250 under our mention of a new unit from last fall and $228 below the lowest total price we could find for new one today. It features a 3840x2160 native resolution (four times that of 1080p TVs), LED backlight, G-sync, DisplayPort, and four USB 3.0 ports. A 90-day Acer warranty applies.