I thought you were in the US, I was going to suggest going to local stores, like hardware stores. My local Lowes has some good ones. No idea about Australia though. I think sheds are usually expensive but it depends on what size you want. I want a aluminium/steel 10x14 shed and it'll cost about $600.
Other than for animals, I'm not sure why anyone would want a wooden shed. The wood would end up nasty too quickly, at least where i am it would. I like things you can wash and that won't rot, get fungus on it, or vines growing on it.