Welcome rtab, that’s a sweet HT (Von Schweikert/Cary) setup.


You’ll definitely want a sub(s) that will complement it. The size/quantity of subs relates to your room’s attributes and your expectations. Your room is not overly large and it seems you have designed the room to account for room mode issues.
Multiple subs are generally used to aid in flattening the low end response. Although an EQ device for the bottom-end, like a Velodyne SMS-1, paired with a single quality sub should do the job as well.
http://forums.audioholics.com/forums/showpost.php?p=401065&postcount=43 The previously mentioned subs as well as the
SVS PB13-ULTRA are among the top contenders in your budget range.
BTW, my HT space is 3600+ cu. ft. and since I added my dual SVS PLUSes last fall I’ve been in HT nirvana. Can’t wait to see pics when it’s completed!