There was (is?) a subreddit called UncleBens, where users talk about using a pouch of Uncle Ben's microwave rice to grow mushrooms.
Apparently, it's the perfect growth media for low budget shroom cultivation.
I don't know what other things you'd need, like temperature and humidity control, and keeping everything sterile after inoculating the rice might be an issue as well. I never spent a lot of time looking at the subreddit, I just know it exists.