Firstly, please don't contribute to giving car audio enthusiasts a bad name. They are cracking down on us everywhere because boomers drive around in residential areas with their systems on blast and annoy people. Be considerate that not everyone wants to hear your car from a block away, some of us need to study, work, and sleep to get on with our lives.
Secondly recognize that you can't have a system which is cheap, loud, and has good sound quality. If you want both loud and SQ, you need to spend some money. That would start with a new head unit. Think about it: what part of your system is actually playing the music? Even the best sub and amp are not going to sound good without a quality signal going to them. And as others have said, if you drive around blaring your system, people are going to know you have it.
That said, if you want to get loud and sound okay, the PG RSD comps are a good starting point. You'll need an amp that puts out at least 50 watts RMS x 2 to power them. Then when you have that sounding good look into some subs. If you buy stuff used you can get a much better value for your money.
