There is no way to effectively add power to a 2.4 on a budget. You really have to ask yourself if more power is that important to you, because the most effective way to add power is to replace the whole car with a RedLine.
That said, I have a 2.4 and a RL, drive them both and enjoy them both, and if I had to part with one of them it would be the RL.
Sky NA 2007 Midnight Blue
Sky RL 2008 Carbon Flash - Naked