Want to put a new audio system in my truck?

Hey, My truck is a(1999 Ford F-150). I want to put a new radio in it and a sub woofer. I am a complete noob in car audio and would like some suggestions, however, my price range is limited to 200$. My next question is where would I put a sub? On the bench? Underneath it?(its only like 6" tall from the ground, not sure if that helps lol) thanks in advance!