A room that size, you are pretty much looking at 2-4 subs. especially if you want to keep the price to $500. One $500 will work but the whole room won't be filled overly well and you will be asking alot from that lone sub. I would start with the one $500 and then, when funds allow, add a second and then go from there. A place to start might be a couple hundred dollars more in the MFW-15 or any of the $500-700 subs from SVS, Epic, Elemental Designs, Hsu etc. All are listed on Craigsub's list.