500 sq.ft. is a pretty big space. One of any sub under $500 is going to have a challenge. That said, both the Klipsch RW-12d (frequently on sale at Newegg.com for $300 or less, plus shipping) and the SVS PB-1000 ($499, shipped) are solid options. Another sub that is reputed to have pretty strong output and decent extension is the Premier Acoustic PA-150 (currently $425, shipped, at Amazon.com).
Not sure what the EMP Tek ES10i10i's output is like, but it certainly doesn't dig very deep (30-150Hz +/-3dB). I'd pass on it.
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