If your measurements are correct you've got a pretty big space. If coin is the issue, I would recommend the Hsu VTF 3 or VTF 15s... dual drive packages. They are the same driver and amps, just different cabinet/port tuning as I understand.
Even two PB2000s would be underpowered for your room... you would need to look at PB3000 I think for SVS to start making sense.
Most of the Subs in the list you see from us here are what you have listed: SVS, Hsu, Outlaw, Rythmik, PSA, Monolith, and if you upscale a little, JTR, Seton, Deep Sea, Funk...
But for the more affordable options, the main thing you need to pay attention to is how they match up to your room size. If the output is clean, and powerful enough to fill the space, you are largely good to go. Secondary is connections through the Amp on the sub. Sometimes people want pass through or line level inputs... just make certain they are going to work for your situation, and enjoy!