Walmart offers the Spa Sensations 10" Gel Memory Foam Comfort Mattress in Queen for $159.99 with free shipping. That's $49 under the lowest price we could find for a comparable mattress elsewhere. It features a 2" top layer of Theratouch gel memory foam, a 2.5" comfort foam layer, and base layer of high-density support foam.

Update: Specs corrected.