I know that the expo that did happen wasnt cheap... venue was expensive, insurance was also right up there and then there was some $20,000 spent on advertising it... radio, posters etc.
In all honesty, i think making anything like this happen in Aus is fraught with hurdles due to the amount of red tape that we have to wade through to do anything... if you got each visitor to sign a personal waiver before entering it could simplify things but personal liability, fire, electrical test and tag make it all a bit of a mine field. from memory, the power supply at the 09 venue wasnt big enough... all these things cost $$$'s
