$2-3k will go pretty quick when looking at the system as a whole.
I would look at a few options for a decent electrical first.
Start with a an upgraded alt(Ohio, mechman, DC, Singer....many others), at the same time upgrade your big three and get what ever wiring done you need. Upgrade your front battery and start to think about what kind of power you may be wanting to run as well. Then pick up an extra battery or two and you will be set for just about anything electrical wise.
After all of that I would look at a few options for stereos. My personal choices and what we sell the most of is Pioneer and Alpine. Mids/highs will boil down to what amps you get and what your goals are. I would look at some good components at least though. There are endless brands that will work great for the application.
I would look at a subs and such last. If you do well enough on the first half the system you can start with a modest sub stage or go crazy and you should have the electrical and mids/highs to stick with the bass.
As for prices, they are all over the place. We sell many brands our self and can ship items as well, but it comes down to what will work best for you and what product/goals you have.
So before we start running through options lets take a minute to figure a few things out.
1. Are you wanting to go single or double din for the stereo? DVD and/or Navi?
2. What are the overall goals of the system? This will help us figure out electrical and a game plan for amplifier power.
You have a large amount of space to work with, so I don't think that is going to be an issue. Just making sure your money is spent in the correct areas will go a long way with this application.
I know I left off deadening the truck in my little list up there, and that comes into play as well, but that can be based a bit on goals and worked into the budget as you move along.
