Sir u should be glad tht u could get to hear quality in ur budget and above all afford it. And no ur car wont become a boom-box but would please ur ears pleasantly. Its just front components to give u a feeling of a "front-stage" and cover the mid and high frequencies in music and the subwoofer covers the low frequencies, without these u cant be able to hear "complete" music.
Now u want it loud or not doesnt depend on a subwoofer being present or not, it is very important so u be able to hear all the sounds in a song.
Sealed subwoofer boxes are meant to compromise on half the loudness to give u twice the accuracy and sound quality.
The system i suggested in previous post would be ideal with that crisp Alpine USB player but if u think those r too many equipment and sound quality doesnt matter to u,
get Pioneer 4350DVD touchscreen player with USB option etc atleast its a branded and nice quality DVD player but there wont be NAV.
Pioneer 4350DVD - Around 38k
Rear Cam (Get the infrared one or the one tht has an led-light) - 2500
Speakers Pioneer D6902R - 8000
Around 1500 for wires and fitting.
=50,000.