LINK HERE Please, if you are serious about learning everything "wrx", please read it. The members will be a lot more willing to help if you show the motivation to learn about your car.
In my opinion... if you are strapped for cash... DON'T waste money on any of the following... BOV's, Turbo Timers, CAI, Injectors, none of that stuff will do you any good right now.
The absolute best mod for power to start with is a catless uppipe. There are a few 'free' mods too.. they won't net you much power though... You said you have a 3" exhaust..are you talking from the turbo back, or just a catback?
Basically... you have to pay to play : )
Uppipe - 150-250
Accessport - 695 new ??? used
Full turbo back exhaust - 500-1200 depending on brand and if new or not.