Smitty, hello and welcome to the forum!
That's a pretty big room that you have there. How tall are the ceilings? One important parameter when picking a sub is the volume of the room.
When looking at bang-for-the-buck subs (which you'll need to fill that big of a room anywhere near your price range), the top contenders that I've seen listed here are SVS, Hsu, and Onix (from av123.com). They are internet direct companies, and you save some money going that route. In addition to recommendations from here, I'd suggest that you e-mail those companies with your room specs and ask them which of their subs that they'd recommend. I've had great luck with responses from SVS, and I've heard good things about the other two companies as well.