Electronics Expo has the Polk Audio PSW125 12" Powered Subwoofer (Black) for $212 - 4% off with coupon code GOGREEN + $20 shipping = $224 shipped. Features 12-inch dynamic balance composite woofer driver, laser-based Klippel measurement technology, 32Hz - 225Hz response, and 300W power rating.
Having had this sub and recently upgraded to the PSW505, I can say the 505 is a MUCH better sub for only $26 more:
http://www.newegg.com/Product/Product.aspx?Item=N82E16882290130