Sleep With Memory Foam 2 Night via eBay offers this 10" Traditional or Cool Queen Memory Foam Mattress with Mattress Cover and Two Pillows for $289.99 with free shipping. That's the lowest total price we could find by $100. (We saw it without the two pillows for $40 less in August.) It features 2.5" of viscoelastic foam on a 7.5" polyurethane base.

Update: The cool memory foam mattress is out of stock.