well first of all dont go cheap spend the money on the parts now and u'll be happier later.. as for power options the list is below different manufactors vary the price and the gains

cold air intake (with or without bypass ur choice)
4-2-1 stainless steel (u can get ceramic but tend 2 crack)
full cat back exhaust (if not axle back w/ custom 2" piping)
high flow cat
upgraded clutch