I have no idea about all this car speaks, subwoofers, and amplifiers and I don't know what I need. I want my car to bump hard but need help finding stuff to make it that way cheap. Around $200-$400 is the amount I'm looking for. Maybe some links to the stuff I need would help. Thanks.
here's a great resource to learn about car audio... http://www.bcae1.com/
You can learn a lot from reading through these forums for a little while too. Then fire off your questions and we'll do our best to answer them. People here are very helpful. For $400 you can have a system (if you learn how to install it properly yourself) that will make your car bump.
with that cheap of a budget, you're pretty much limited to keeping the factory radio and speakers, and adding a pre-amplified subwoofer, like an SAS bazooka tube (amplified) or Infinity Basslink. you'll also need an amp wiring kit for that.