If I had a $1k budget for a sub, I would go DIY. I would go for either a
Mach 5 UXL driver, a 1 kW Behringer amp, and a miniDSP, or a couple
SI 18" D4s and an iNuke amp with a miniDSP. To save a few dollars I would look for a used amp to keep the whole budget under $1k shipped. Those setups would absolutely own any commercial subwoofer you can buy at twice the cost. However, they would be a bit of a project to put together.
I would tell the OP, if he isn't interested in making a big project out of it, check out
this kit. It is under $1k delivered and isn't a big project at all, because all you have to do is assemble it. The hard part is already done. All you need is a screwdriver, some glue, and maybe an hour of assembly time. The drivers will be fairly high quality ones, probably better than what you find in Hsu and Outlaw subs and certainly better than what you will get with a PSA sub. For a better driver in a commercial sub, you would have to look at higher than $1k subs, and with the Dayton kit you get two such drivers. This means low distortion, high output, good linearity, good compression behavior, and high sound quality.