Are you looking for the perceived "best" manufacturer, or someone to build and modify a car to suit your taste?
If it's the manufacturer that you want opinions on, it has been discussed at length before, but I'm sure you'll get more opinions on this thread.
If it's someone to build the car for you, while not in Vic, I have only good things to say about Scott Hampson from Brisbane
http://www.venomcobras.com/ Scott is able to build any model to any budget. His cars have picked up numerous trophies at shows if that's your thing, and he's also had a lot of experience in setting up cars for the track.