Mushroom spores are legal in most US states because they don't contain psilocybin (in contrast to cannabis seeds being illegal - they contain trace amounts of THC).

You used to need a pressure cooker and a lot of supplies. However, with the advent of the Uncle Ben's method, you just need some bagged rice from the store, a legal spore syringe purchased online, and a bit of curiousity, community reading, and time. There is a subreddit dedicated to it: /r/UncleBens

Many choose to innoculate in the bags and then transfer to a fruiting tub, but it works just as well if you never remove them from the bag - just a smaller yield. Perfect for you and a couple friends.