mose, check my ts.com page for what I have in my truck and how I did it.
OP-Yeah, dont skimp on h/u. That should be one of the first things you do. Pioneer DEH-5900 is a wonderfull h/u with full controls and display for like $170.
Front speakers should always be quality. Rear speakers arent needed in most applications, I always leave them stock and run off the h/u power in my installs. Front stage speakers should be components and some good brands are CDT, Alpine, Elemental, Pheonix Gold. You can spend from $100-$200 on these.
Front speaker amp should be about 100x2 and can be any model from a reputable brand. No Boss, Legacy, Pyle, Bazooka, Sony, Audiobahn, etc. $100 should cover this.
Sub can be your choice. I would just personally just choose 1 12" for it's all around versatility and SQ. Image Dynamics, Elemental, TC-sounds are some good reputable brands for cheap. Dayton titanic rings a bell as well.
Your sub amp should be at least 300x1 (rms) to get the full benifit from a sub. Again, what model does not really matter. Just get one with at least 300x1 "clean" power and stay away from crappy brands (see above)
Box-plays an important role in sub sound quality. If you buy ones that are pre-fab, get sealed, not ported. Pre-fab ported boxes are tuned really high and have really peaky nasty sounding bass. Build your own ported box port tuned to 30-35hz and you would have a nice sounding system that sounds great and drops some bottom.
Dont skimp on wires. Knutz concepts offers full wirekits at cheap.