Last summer I got my certification from Reef Dive, a medium sized operation based in Airlie Beach, Queensland. Most dive operators in this town are fairly inexpensive, relative to other places in Oz, since they cater to the backpacking crowd (myself included).
Fortunately, with such a good exchange rate, Americans pretty much double their money when travelling through Australia.
If you stay in Airlie Beach, you'll be diving in the Whitsunday Islands area. Expect near 100 ft visibility, warm air temps, 78 degree water temps, and a variety of marine life including sea turtles, rays, and dolphins.
Another popular place to dive from is Cairns. You can catch a direct flight from Sydney to Cairns.
Regardless of where you decide to dive from, a live-aboard package deal is the way to go. That way, you get the most diving in the least amount of time. Hope this helps.
[This message has been edited by Dave (edited 06-04-2001).]