Get an aftermarket ECU,555cc injectors,Z32 AFM, and a good clutch. You already have the turbo so that is the easiest and most cost effective way to get 260-270rwkw.
So cost wise without labour you are looking at:
ECU=$1200-$1700
555cc injectors=$800
Z32 w/plug=$320
Decent clutch=$600-$1000
Modifying a car for more power is not cheap, and if you try and cut corners it will cost you more in the long run. So do it properly first and you shouldnt have too many problems.