It's going to be really hard to find a musical sub at that price. At your budget I think your mostly going to get boomy, flabby sounding subs. Perhaps you could wait a while and save up a bit more cash?
Television: Mitsubishi WD65737 DLP
Processor: Emotiva UMC-200
Amps: Carver AV 806x/Behringer EP4000
Mains: DCM TimeFrame 600 Center: AT 453C
Surrounds: AT 251.1 Sub: Danley DTS-10
Blu Ray: Panasonic DMP-BD655