Walmart offers the DHP Bombay Twin Metal Bed in White for $65.68. Choose in-store pickup to drop it to $39.57. (Amazon has it for the same.) That's the lowest price we could find by $40. It features metal slats, supports up to 300 lbs., and measures 78" x 42" x 40".

Update: It's now out of stock at Walmart; however, Amazon still offers it for $39.57 with free shipping.