I'll second the suggestion to start with oyster mushrooms (which you may still find at some grocery stores) rather than agaricus, but for different reasons.
Oyster mushrooms are really easy to grow. You can buy kits, or you can do it from scratch in a 5 gallon bucket or garbage bag with straw or wood shavings or similar substrates.
Agaricus, on the other hand, are more complicated. They're not primary decomposers like oysters, they're secondary decomposers. Which means rather than using a fresh substrate, you have to grow them on active compost. It's certainly achievable by a dedicated hobbyist, but it's not going to be an easy first time IMO.
If you want a good chance if success, start with oysters.
Edit: oops, just realized this post was months old.
My toes, Sis.