need advice on replacing a sub woofer

I have the Athena Technology Micra M225 Surround Sound system. The subwoofer on it has broken. Can anyone recommend a substitute so that I do not have to replace the entire system (looking to spend no more than $300, used is fine) Here are the specs:


Surround System:
Woofer: 8" (20.3cm) High-Excursion Injection Molded Poly Cone
Frequency Response: 30 Hz 100 Hz (±3 dB)
MOSFET Power Amplifier: 225 Watts 75 Watts (RMS)
Dimensions Standard:
(Height x Depth x Width) 16.7" x 14.2" x 9.4"

My amp is a Yamaha RX-V663:

Minimum RMS Output Power for Front, Center, Surround, Surround back
20 Hz to 20 kHz, 0.06% THD, 8 Ω ...................................... 95 W Dynamic Power (IHF)
Front L/R, 8/6/4/2 Ω ..................................... 135/165/195/240 W
Maximum Useful Output Power (JEITA) [Asia, General, China and Korea models]
1 kHz, 10% THD, 8 Ω ............................................................ .............................. 130 W
Maximum Output Power [U.K., Europe, Russia and Asia models] Speaker impedance setting: 8 Ω, 1 kHz, 0.7% THD, 4 Ω
............................................................ .............................. 145 W Dynamic Headroom [U.S.A. and Canada models]
8 Ω ............................................................ ........................... 1.4 dB
Rated Output Voltage/Output Impedance OUT (REC) .......................................................... 200 mV/1.2 kΩ PRE OUT ............................................................ ..... 1.0 V/1.2 kΩ SUBWOOFER (2ch Stereo, FRONT SP: SMALL)
............................................................ .................... 1.0 V/1.2


Thanks!