How would i get some Cheap But Good HorsePower Gains For My '03 Chevy Malibu LS?

[Jimmy Hoffa]

Only Thing On The Car Now, Is a 1 Year Old 12" Glass pack. And Spectre Cone Open Box Air Filter. Any Suggestions?
I Just Put The Glasspack On Too Get Rid Of That Huge Muffler So I Can Hear My Car Run, And It Has To Help Flow Lol. I Mean That Stock Muffler Is A Coffin Lmao;.