Walmart offers the Mainstays Twin-Over-Twin Wooden Bunk Beds in six colors (Walnut pictured), model no. WM3921, for $169 with free shipping. That's tied with our mention from two weeks ago as the lowest total price we've seen for this bed. (It's a current low by $31.) It can be used unstacked and features a wood slat system intended for coil-spring mattresses.