Main question you should be asking urself is what are you gonna use the car for? Drags or track? How much do you have? A little may be 1 grand to someone, but 10grand to others. Give an average price range. Look for a target power output too, cause you'll need supporting mods and stuff to make the car drivable, safe, and not go boom. EG: If you want like 800 hp, you need BIG injectors, etc, 1 time to settle everything.
If you don't care about anything else and just want extra power. PFC(ECU), EBC, Injectors, Pump (basics). Turbo/engine rebuild.