Not quiet racing but I do the Street Sprints at either Lakeside or Queensland Raceway. Cost is $145 per day at approximately 8 rounds per year. That's 3 sessions per day at 6 laps per session.
You don't need a race car, you just run your everyday street car so only extra cost on the day is fuel and a AASA licence which you can get yearly or just for the day on the day.
So all up it costs me about $220 for the day, pretty good value i think and everyone pays the same.
Also, yeh that was a good episode of Topgear.