First of all welcome to the site. It is an awesome place to hang out here. A lot of cool people and you can learn a lot on here. I am only 17 and just bought my stang like 3 months ago. I would say that your first modification would be like a exhuast system from the catalytic converter and back. This will give you awesome sound and some more power. It would probably be like $300 but im not too familiar with 99's. A good place to go and hang out on here is the blue oval lounge. Have fun!
Later,
Nick
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