Here is my suggestion for a budget friendly but well rounded setup.
-- Pioneer AVH-P3200DVD Head Unit
-- Polk Audio db6501 component speakers
-- Kicker 08ZX550.3 Amp for the components and the sub
-- Kicker Solo-Baric L5 08S10L54 sub
-- Kicker ZCK44
-- Pioneer ND-BC4 Rear View Camera
As for the box you can buy the Zenclosure or if you have some basic wood working skills you can build your own just like it for half the price.
You can run the components off of the HU but you'll be giving them less than a quarter of the rms power that they can handle, you and the speakers will happier in the long run with more power. The 3 channel Kicker amp is inexpensive and has plenty of power for both the components and the sub its worth the money.
The amp kit comes with everything you need to do the install.
You can change the sub to anyone that you would like, look for single 2ohm or dual 4ohm voice coil and around 400-450rms watts it will work great with this amp.
I priced all of these products at sonicelectronix.com
Car Audio Stereo - Car Subwoofers - Car Amplifiers and Speakers, the price came to $1,124.95 shipped and it will include the dash install kit, HU wire kit, and antenna adapter. This is obviously not the most high end system but it will be one that you can be proud of and very happy with for less than some people pay for just their headunit.
I hope this helps and good luck.