Zinus offers its Zinus Gel-Infused 6" Green Tea Memory Foam Twin Mattress for $76. Coupon code "WELCOMESHERPA10" drops the price to $68.40. With free shipping, that's the lowest price we could find by $8. It consists of a 1" gel-infused memory foam layer, 1" comfort foam layer, and 4" high-density foam layer.

Note: The pictured frame is not included.