WHen i got my first evo that is exactly what i did. I bought a cat back, then a dp, lastly the tp. If you are just looking for gains off the bat, i would suggest getting that tp out asap.That is the main reason your stock exhaust loses it power.
I currently am running the ams tbe. I bought each othe three parts separately and it all came to around 700. (cat and dp barely used, test pipe new). Used exhausts are a cheaper way to go...just make sure you get plenty of pictures before hand and evaluate the person's sales rating.
Good luck
