To be honest, you really wont.
Well people have made 300rwkw-320rwkw using Garrett-IW turbos (IW = internal wastegate)
Not the most ideal setup, but certainly the most cost efficient if you are dead set on a number... So i must say...
Lose the 300rwkw "I must have it" in your brain, settle for 270-280rwkw and just get a bolt-on hi-flow, stay totally safe from Police and look factory. Win-Win IMO
Otherwise you'll be spending upwards of $2000 more and I tell you now, for the extra 20rwkw - you won't really notice it/justify the cost.
The way i see it - either go for 350rwkw and justify the $2000+ spent or settle for 280rwkw.
Plus there is everything from brakes, clutch, diff, exhaust etc etc that needs attention and I can say with certainty, you've not really touched those areas