Walmart offers the Better Homes and Gardens Leighton Twin-Over-Twin Bunk Bed in several colors (Black pictured) bundled with 2 Spa Sensations 5" Memory Foam Twin Youth Mattresses in Pink or Blue for $189 with free shipping. (The mattress link is just for reference; you will select your mattresses when you add the bunk bed to your cart.) That's a savings of at least $146 and the lowest price we could find. It measures about 79" x 44" x 65", converts to two stand-alone beds, and accommodates coil spring mattresses only; features include two full-length guardrails on the top bunk and a 4-step ladder.

Update: The price has increased to $199.