Polk Audio PSWi-8M Wireless Subwoofer for $79.99.  Shipping is $5.00 for a total of $84.99 shipped. Here is a screenshot for your reference. It features 140 watts of peak power, copolymer driver, down-firing enclosure, 36Hz to 250Hz frequency response, and 4 ohms impedance. Most places have it for about $116 or more.