VM Innovations via eBay offers the refurbished Kicker 12" Car Audio Subwoofer for $109.99 with free shipping. That's $205 list and the lowest price we could find. It features 500-watt RMS power (1000-watt peak), a 25-500 Hz frequency response, and 2-ohms impedance.

Note: A 90-day warranty is included, although it's unclear who supports it.