It's a long-standing policy that if you contribute to a conference, you receive free entry. The easiest way to contribute is to do a talk, and until the end of June you can set that up by responding to OSDC 2009's call for papers.
This year's Open Source Developers' Conference (OSDC) returns to Brisbane between 25-27 November and covers all things open source with a traditional focus on Perl, Python and PHP content.
If a full talk is not your thing, I can recommend getting started with a lightning talk, which is a short five-minute talk that can at once be highly entertaining and very rant-like. A good example is Jon Oxer's series of talks each year about OSDcLang, which last year found its way onto his Mazda RX-8.
Full details and instructions for your submission can be found here.