The visa you might be thinking of is the Electronic Travel Authority for tourism obtainable for less then 90 days.
You could probably get a good deal going into one of your discount travel agents locally to get airline tickets and keep things open.
Unless they throw in a few nights stay in a package.
Then when you get here there are good backpacker hostels or inexpensive motels outside of the city areas.
Jump online to find a cheap second hand bike with registration and roadworthy near to where you might fly into.
Then you are set. If you are only going to be here 4-6- weeks then maybe stick to Qld and NSW.
In other words fly into Qld and bike around going up north then ride down to Sydney along the coast, sell the bike and see Sydney flying out from there. Just a suggestion.
Edit - lurker, long time. 
tell em your an expert fruit picker they'll just wave ya through.
I watch those shows too, zanadoo.
It has inspired me to use packing cells for most of my things. Keeps the suitcase looking very tidy.
I'd hate to have to open a suitcase on camera and have all my stuff tumble out.
Main thing I think is to read the form and declare anything you even remotely suspect might fit into their categories. That way, they can check if they wanrt to and decide.
Basically if you try to avoid food and wood, you're pretty right.
If you have prescription medicine, keep it in its original chemist box with your name on it etc and it's worth having a letter from the doctor with a list of what medication you are on and why. I guess that really only applies if you're getting older and have quite a few medical conditions though. When we travel, my husband has almost a whole carry on full of his medications and we've never had the slightest trouble as long as customs can see it.
i found a company who might help you
looks like a well run organisation
