Considering my budget I went with:

Boss Audio BASS600 8-Inch Low-Profile Amplified Subwoofer (This does fit under the passenger seat)
JVC KD-HDR50 HD Radio CD Receiver / USB 2.0 / iPod/ MP3
Pioneer TS-A6882R 6" x 8" 4-Way 280-Watt Speakers (4 total)

Total: $357 :)

I'll have to wait a little while to get an amp. Homies be broke these days. I'm not going to bother replacing the tweeters unless I notice a gap on the high end.

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Happiness is: a belt fed weapon