Intake: AEM - $160, or Injen $200, or Ebay Intake $50-$60. They all offer roughly the same gains/sound
Exhaust: If you have an MP3 you don't really need to do it, but a decent exhaust might get you some gains. $350-$600
Header: $200-$500 will be your best mod it seems.
So for $600-$1300 you can get the three depending on your choices.
Intake nets about 2-3whp, header prolly 10whp, exhaust 4-5whp. All of these in a system might net you 15-20whp.
Those are just my rough figures, obviously I don't know exactly what it will cost/gain.
Chris