I can only give you second hand experience on JBL subs. We bought the 150P for my sister because she already has all JBL speakers and wanted to buy locally (need it now, kind of thing.
) I generally like JBL and still have 5 JBL speakers, just never personally owned one of their subs.
I think it is pretty good, but it won't go as low as some of the HSU or SVS subs. It has all the standard connections (line level and speaker level) and the internal crossover can be disabled if you hook it up to your receiver using the sub pre-out and want to use the receiver's bass management. It was a breeze to calibrate and integrate with the rest of the speakers.
Other than the HSU-STF-?? that you can now buy at CompUsa, I don't think you can get a HSU or SVS in your stated price range. IMO, the best of the bunch is the SVS PB10-ISD ($429) and I'll be getting one as soon as I move. Alot of people seem to like the Dayton subs, but for my money, I'd rather go with a name that has been making speakers for decades (JBL) than the 'house brand' (Dayton) from PartsExpress.