Iv'e heard some guys saying they can make a sub for $500 that will crush $2000 ID subs.
I am sorry if there are a million other posts like this, but I am having trouble finding what I am looking for. I'm sure some of the experienced DIY'ers will have some great suggestions for me.
I am not one of the experienced, but it will help others to help you if you state your limitations in both budget and size. For instance, a $500 sub that will crush a $2000 ID sub could be the Tuba HT, but it's freaking huge. You could also use a plate amp, because it's so darned efficient. If it absolutely has to be a plate amp, I think you most likely will want to stay away from sealed subs, because they require more power for the same output, generally, especially for the lower frequencies, and more so when the cabinet gets smaller.
jliedeka has recommended Home Theater Shack for ideas.
http://www.hometheatershack.com/forums/diy-subwoofers/
If you have an attic, or some large space/basement under floor, you can learn about infinite baffle subs. Little to zero space taken up, as only the drivers are visible (if even visible):
http://ibsubwoofers.proboards.com/index.cgi
If you were willing to spend as much as that soundsplinter (which I have no clue about), you might be getting into JL and LMS territory as well. Depending on your design, you may not need that kind of capability, and if sealed, well, I don't know if a plate amp can do justice. But, I don't know jack.
A nice bang for buck sub, without being grossly oversized, is the Kappa build, the first sticky in this subforum.
Just wanted to respond, since others who are more qualified haven't chimed in yet.