For simple bolt ons on a budget, get a good cold air/short ram intake(AEM, password JDM carbon, fujita), DC SPORT JDM type r header, cat back exhaust mainstream will custom make you a good one for a very competitive price that flows excellent, AEBS intake mani, tuning(VAFC, or chipped P28). That would be the cheapest route to realize some decent gains. It won't make a ton but make it a little funner.