Walmart offers the refurbished Samsung 55" 4K 2160p WiFi LED-Backlit LCD Smart Ultra HD Television, model no. UN55JU650DFXZA, for $579.99. Choose in-store pickup to avoid the $49.97 shipping fee. That's $20 under our mention from June and the best price we've seen. (It's a current low for a refurb by $99.) It features a 3840x2160 (2160p) native resolution, quad-core processor, WiFi, Internet Apps (like Netflix, Hulu Plus, Pandora, and Amazon Video), USB, and four HDMI inputs.
Note: A 90-day warranty is provided, although it's unclear who backs it.