Newegg offers the Acer 28" 2160p 4K LED-Backlit LCD Ultra HD Monitor, model no. B286HK, for $349.99 with free shipping. That's $50 under our mention from two weeks ago (although that was bundled with a laser printer) and the lowest total price we could find now by $110. The monitor features a 3840x2160 native resolution, DVI, Display Port, and USB.
If you haven't yet, use Newegg’s Android app and pay using Google Wallet to cut it further to $334.99. (This discount can only be used once per account.)