Polk via eBay offers the Polk Audio 300-watt 12" Powered Subwoofer in Black, model no. PSW505, for $159.99. In-cart it falls to $143.99. With free shipping, that's $16 under our Black Friday mention and the lowest total price we've seen in nearly two years. (It's a current low by $36.) It features a frequency response of 23Hz to 160Hz, magnetic shielding, phase switch, and adjustable crossover.