Have Jim build you a Rythmik 15" or dual passive 15" sub. I dunno what Jim and Brian (from Rythmik) charge for the dual passive, but I bet it's unbeatable for the price. I think someone said it could be tuned to 18Hz, and with room gain it'll probably go flat to darn near 10Hz.
The PB13 Ultra is a great sub - the only ported one I've heard that I like when playing music. If going sealed, though, I say have Jim build you one, or a passive sub. You could also bump the budget to $2000 and get the best sealed sub around - the Seaton Submersive.
Oh, and I completely agree about EQing the sub. It's a necessity for music.
Enjoy the search.