Polk Audio PSW110 10" Powered Subwoofer for $124.99 shipped.  Here is a screenshot for reference.  This subwoofer features 200 watts of power output, 10" driver and vented, downfiring bass port, adjustable 60-160Hz low-pass crossover and phase switch, line level and speaker level inputs, and 32Hz to 250Hz frequency response.  Most places have it for about $149 or [...]