Late to this party but here is your go to shop in perth - https://www.facebook.com/gsautoworksau
GTSBOY is on the money cost wise, drive in and out will cost you 15-30k or more.
Some items that will save you money
- plug in link ecu g4x is much cheaper than haltech.
-Pulsar turbo, seem to be "OK" now, never used one myself
You really don't have to build the motor, E85, headgasket, studs and a good RB26 will live for ever.
Swapping over the twins won't save much as you still need ecu, tune, fuel system etc.