And when it comes to the box, don't give in and use a factory box. Build your own, make sure it'* the right volume, and port length/diameter for your specific subs, and use quality materials, like high-density fiberboard, at least 3/4" thick. And skip the plexi windows if you want really good sound.

HU (100) 550 left

Wiring kit (30) 520 left
http://knukonceptz.com/productDetail.cfm?prodID=KLM-K4

Wire and connections for Big 3 (20) 500 left
get any Knu 4ga and ring terminals

box building materials (40) 460 left
assuming you can build your own
There are lots of choices for subs and amps.
Depends if you want to go ported or sealed?
10"* or 12"*?
one ot two subs?

And caps are pretty much worthless.
If you have dimming problems get a larger alternator and/or add a second battery

Two 12 inch subs, which is better sealed or ported?

For going in a trunk, I think sealed is the way to go. You should also baffle your rear speakers for clearer sound @ lower bass levels.

Check out ebay for buy-it-now stores that have new but discontinued components. I saved a ton of money going that route, and what I have is in my siggy

if you want any truck space left then you will likely want to go sealed.

you can look into eclipse or maybe the TC sounds DB 500. 110 /12" shipped

leaves you with 240 for an amp and misc stuff you may need.