How much power are you putting to them? If you wanna be anywhere near as loud as those videos, you will need a giant amp, and good subs.
That being said...you will need 1/0 cable for power/grounds, H/O Alternator, batteries to power the amp.
If you just wanna make your setup louder...you can build a better box. With a 4th order, you will have a flatter response over a wider range of frequencies. Also, do the big 3 upgrade to beef up your electrical.
Just my $.02
Edit: just saw your budget. New subs/amp. Do 2 18s imo. No reason to go with less cone area since you are in an escalade. And definitely build your own box.