Pretty easy really, no booking just roll up on the day. It was actually $30 last time in January, but whoop-de-f**king-do.
No fire extinguisher requirement, just show up with a road/raceworthy car, clothes that cover the extremities and a helmet. That's it. Last time there was every car there from a bog stock Hyundai Excel to a 996 Porsche Turbo, a stripped out supercharged V8 M3, what looked like an ex-V8 Supercar and Scotsman's 33.
I found it to be a great introduction to track days too, because everyone is out there just to have fun, not set times. The first few laps you'll be paranoid as hell about other drivers and binning it, but after that you catch yourself having fun and it's all good after that
It gets pretty busy in the morning, but if you're prepared to stay the whole day and get back to melbourne late, you'll just about have the track to yourself in the last couple of sessions.