Polk Audio PSWi-8M Wireless Subwoofer for $99.99. Shipping is $5.00 for a total of $104.99 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 $149 or more.