Like somebody said, I'd stay away from the square subs unless you want to kiss your trunk space good bye.
My audio history: I used to be like you, but without the $$ to throw around so I started small and used. Which quickly taught me the fundamentals of specs and box building to get the most out of what I had. Then I went through the competition stage, I used a variety of of subs, but always Hifonics amps. Competitions were fun, but for normal driving and enjoyment, it was just over kill. So once I graduated from college I worked for a place called CIS
www.CIS.com where we would handle stolen stereo claims for insurance companies and replacing the equipment, So I was very knowledgeable on what was out on the market.......4 years ago.
Now, like I said before, companies are constantly bought by better/worse companies in the audio world and equipment will be better or worse than it was a year ago without warning.
The best advice I can give is that the box is what makes the speaker. I like my trunk space because I'm a hockey player and need a place to throw my stuff. So since my competition days I've been an advocate of the small sealed box. I am a huge fan of Diamond Audio subs. Especially the D6 series. Very high quality and its specs only call for 0.5cuft. They are fairly inexpensive as well, through my hookup at CIS I can get them for around $160.
Other than that for subs I would recommend Elemental Designs, Adire Audio (although I just noticed they are shut down). With your bank roll dedicated to a system, the best recommendation I can give is for a single JL audio 13W7. and a
QUALITY, true 1500w amplifier or a 12w7 and a quality 1000w amplifier.
For amplifiers, I'd recommend Hifonics, Crossfire, JL, phoenix gold, Xtant, One good used one to look for is a JBL power series or Precision power art series (as mentioned before).
Does anybody know if soundstream is any good still? Also how about Alpine? I know shortly after I bought all my Alpine stuff Alpine started dealing with Best Buy which really limited the amount of product available to its usual dealers and I heard Alpines quality suffered as a result of trying to keep up with demand. Can anybody vouch for that?