Well first off you can't do things on the cheap if you have an STI
So you will need.......................
Motec = 4-8 grand, depending on how it's tuned,
Defi guages = 3-4 g,
PPG gear box = 4-6 g,
Front mount = 1-2 g,
Exhaust = 1-2 g,
Bigger turbo = 1-1.5 g,
18" Wheels & tyres = 2 g,
Sway bars & links = 1 g,
Coil overs = 2 g,
Pod = 3-5 hundred,
Driver training ?

Come on cheque book racers, what have I forgotten?????

That should take care of about $15,000 - $25,000 Then sell it in 12 mths because it's an uneconomical, unreliable, uncomfortable pig for about what you paid for it. hehe
Enjoy.