Was at my local Bunnings this morning and they had Mr Fothergills White Button Mushroom growing kits for $10, down from $25. Might be nationwide if other stores still have stock.
Since a single kit is expected to grow several kg of mushrooms and it's almost idiot proof to setup and grow them (open the box, pour the included bag of dirt on top of the base layer, then spray with water every couple of days), you should at least break even given the price of mushrooms at the stupidmarket is already $10 per kg.
They don't even take up mushroom in your shed (or whichever dark cool place you put them). You could even store them on top of a cupboard if you're stroganoff to lift it that high. So try your luck and see if you can turn dirt into food - like magic!