This best-selling 8" Spa Sensations Memory Foam Mattress drops as low as $139 at Walmart.com. Plus, shipping is free. This matches our mention from early December as the lowest price we've seen to date and over 3,200 reviewers have given it a perfect 5 out of 5 star rating! The Full size drops from $199 to $139, Queen drops from $239 to $189 (it's going for $255 at Amazon) and King and Cal King drop from $259 to $199. Sales tax is charged in most states.