Walmart offers the Mainstays Twin Over Full Bunk Bed
, model no. 4055019W, for $135
with free shipping
. That's $25 off and the lowest total price we could find. It accommodates one twin and one full-size mattress (both sold separately) and features a steel frame, guardrails, ladder, 200-lb. maximum weight capacity for upper bunk, and 450-lb. maximum weight capacity for bottom bunk.