exhaust upgrade

ok im gonna upgrade my exhaust, but do it slowly. Headers, Cat and muffler, not that order but thats the stages. Anways im prolly gonna do my first upgrade this week, looking to spend about 200 bucks or so. Im looking for HP right now more than anything. So what would be the best thing to upgrade right now, the headers, the cat or the muffler? Also keep in mind the dont want the car to sound like a rice burner in the end. Suggestions on items to buy are appreciated.

2.5 inch catback to a Dynomax muffler