Shew....you'll be hard-pressed to find cheap mods that bring out more power from ANY normally asperated engine. Complete intake you're looking at 10hp at most, full exhaust would be more of the same. Any reflash would net you better gas mileage than hp
Unless you want to spend big bucks, you won't make big numbers.
Or you could just take a shitload of weight out and make the lb/hp number lower and thus you will be faster