I think one of the best deal out there for 2K is the
Seaton Submersive. I don't know of any sub that can outperform it at that price point. It is regarded by many as one of the best subs available at any price.
Something else to consider is the
Elemental Designs A7s-650. Just look at that
frequency response chart; that is excellent performance! It is a newer design so there hasn't been as much customer feedback yet, but I just know that thing is going to be a absolute beast.
Another intriguing sub from Elemental Designs is the
P7-650, which is kind of a dual-drive design. This will help mitigate room issues more than just one sub, so you will get a more even listening experience where ever you are listening from. It also has phenomenal output. This will be a SPL monster if set up correctly.
If you stretch your budget a bit, you can get a
Hsu ULS-15 dual drive. It has the high output and sound quality of the Submersive along with the all the advantages that come with a multiple sub solution. This is what I have and it truly rocks.
Also, if you look around, you can get a Deftech Trinity for less than 2K. It is supposed to be able to hit 128 db at 20 Hz and 116 db at 16 Hz in a normal room. That is insane, and may be the very best non-internet direct sub out there.