horsepower gains for 2004 ranger

[indevincible2]

I have a 2004 Ranger Edge 4.0 liter. I have 500 dollars to spend for engine modifactions but i dont know what to get that would be the best for my truck and would give it the most horsepower gains. My truck is a lease vehicle so i can not do anything that will be too drastic such as exhaust just things i can take off after a year. I would like to buy a new chip although i could not do that untill a tuner comes out because my newer truck has something that wont let me get a chip with out a tuner. PLEASE HELP me wit suggestions.
I currently have blue neons throughtout the interior and underbody, halogen lights, 2 10 inch subwoofers and 1 6 1/2 inch subwoofer, blue suede interior, but i am now looking for items to increase my horsepower.thanks

[2000mudder]

its not yours to mess with. you shouldnt waste money on something that isn't yours unless you plan on buying it after lease.

[indevincible2]

i plan on buying it after it is over, although just incase i dont wanna do anything that changes it afterwards.