Walmart offers the refurbished JVC 55" 4K 2160p LED-Backlit LCD Ultra HD Television, model no. LT-55UE76, for $276.66 with free shipping. That's tied with our March mention as one of the cheapest 55" 4K TVs we've ever seen. (It's $133 less than a similar refurb sold elsewhere.) It features a 3840x2160 (2160p) resolution, LED backlight, USB, and three HDMI inputs.
Note: No warranty information is provided, although Walmart offers a 90-day return policy.