Well fortunately for you, there are lots of subwoofers out there of decent quality of all shapes, sizes, price, etc. What did you have in mind for any of these attributes? Room dimensions? Usage?
From the gossip I here, the best in that price class are probably the Bic H-100 (who knew they made more than razors!) and the Onix X-Sub. The X-Sub would likely be your best bet in terms of overall quality however.
How big of a room are you looking to fill? What will you be playing?