That is a very large space you're dealing with. You should plan on adding a second sub at some point.
Options (one now, another one later on) include:
- SVS PB-1000 ($499, shipped, with free return shipping within 45 days)
- Rythmik LV12R ($589, not sure if that includes shipping)
- HSU VTF-2 MK4 (currently on sale for $529 + $67 shipping)