you won't get much for $200.00. Most kick *** head units alone exceed this price. You can get a budget one for $99.00 but you'll have nothing left to put into amps, speakers and subs.
If you just want some boom. You can always get a sub and an amp. Some of the cheapest subs you'll find will run about $80.00. You'll barely be able to get an amp to power it for under $149.99. You'll still need an enclosure and installation.
You may just want to roll with your factory sounds until you have more like $500-1,000.00 to really build a 1/2 decent system.