17X24 room, you want it loud, and your trying to keep it under $500?
I don't know what your idea of loud is, but I don't know how you are going to do it given your budget. As the other poster noted the BIC DV62si and 62-CLRS would be a start. I wouldn't get the BIC sub, I would get the Parts Express Sub 120. It's currently $148 shipped for a 12" sub with 120watt amp.
I think the iron triangle of business is at play here: you can have it: Done Right/Done Quick/Done Cheap. Pick two.