SVS are Outstanding engineered subwoofers w/ Awesome performance. But that comes at a cost. Your not going to stay under $400 and fill a 1000sqft space. I would recommend the PB2000 if your going to stay with SVS
The PB-2000 Pro subwoofer features legendary SVS technology for immersive home theater experiences.
www.svsound.com
If $400 is the max budget i suggest
rslspeakers.com
Or save until you can get the SVS