Steve gave some very good advice. You won't get realistic bass without a subwoofer. The best a 6x8 or 6x9 can provide a decent lower midbass.
Where I would differ with Steve is in the speaker placement. I would put the midwoofer in the door and midrange/tweets in the kick panel. It'll improve the imaging.
My personal recommendation would be the following...
Head Unit: buy the 300.00 HU that you like the best from a brand like Nak, Alpine, Sony, Pioneer or Clarion.
Front Doors: Eton 8-480/32 8" 136.00 per pair. Adire Audio AV8 is an option at 120.00 per pair.
this may may take a small amount of modification but 2 8" Adire Audio subs would be a perfect option. Not released yet, but the prototypes have been very promising. Pricing to be announced. probably expect 180.00 for the pair.
Kick panels: Vifa Car system from Madisound. 130.00 per pair.
Rear doors: Vifa mids from component set above. 45.00 or so.
Amp: Look for a 6 channel amp from either PPI or a/d/s/. Preferably at least 50 watts per channel. a/d/s/ PH 15 would be a great choice. 300.00
Crossover: Look for an Audio Control 3xs. Should be 80-100.00.
The 8" speakers should give you some decent bass, especially for their size.
summary:
HU: 300.00
Front door: 150.00-200.00
Rear door: 45.00
Kicks: 130.00
Amp: 300.00
X-over: 100.00
dynamat/installation/wires: 450.00
Total: $1475.00-1525.00
