Options...
A couple of weeks ago I did some research and got some feedback in
the link here you may want to take a look at. All but one listed fall into your price range. The Dayton Titanic might give you the biggest bang of these, but is also right at your limit, whereas some of the others may be enough for you w/out getting to that point.
In addition to the ones I'd listed, the HSU STF-1 would also fall in your price range. I agree with J that an SVS PB10 would be all you'd need, but being $429 w/o shipping is a bit out of your price range.
One other option is to consider used on Audiogon, eBay or any for sale on several home theater forums. I've gotten several HT components used and had great luck w/them... -TD