ok, well it depends, do you need the piping done or are you going to do it yourself?
In Sydney Ricol performance will install a 600x300x76 PWR core tube and fin intercooler for $1800 drive in, drive out. This is with your choice of stainless or alloy piping.
If you can do the piping yourself Mr Enforcer Engineering sell PWR core tube and fin coolers 600x300x76 polished for $900.
If you are after a bar and plate core Hyperflow Intercoolers in wollongong are very well respected but they cost.
You dont really have to buy an intercooler from Sydney also because most of the big suppliers ARE, etc will be able to post an intercooler fairly cheaply.
There is an awesome article on www.are.com.au about intercoolers you should read before making your decision. Also second hand is a great option.
I just bought a 640x220x90mm Hyperflow tube and fin intercooler for $700 second hand and never used with tanks, polished, etc. When I rang Hyperflow they quoted me $980 for the same cooler new so it was a great saving.
Good Luck,
Evan