My sentiments would be the same as most of the other posters here. Buying a smaller, inexpensive sub, while providing you with some low end in the short term, will only result in you buying a replacement in a short while.
Having said that, I'd say Mazer's suggestion would be the closest you could come to what you're looking for at that price tag. There's also an
Athena AS-P4100 available from Audio Advisor for $149 (shipping not included) that might be a decent solution for you in the interim. I had (still have but not using) the predecessor to this sub and for what it costs, it does a relatively good job assuming you're expectations aren't too much and you're not using it in an overly large room.
If there's any way you can hold off to at least save up closer to $300, you'll do much better, but if not, try one of these two for now... -TD