This is from the first grow I did, PF tek style but with a few updates. I did a couple monotub grows a year later that went great but I can't for the life of me find any pics.
The white pebbles are perlite and the cake is mostly rice bran meal and fine vermiculite, with a little coffee and gypsum.
Sterility will only become a barrier when you move up to things like sawdust colonies that are too large to deal with in a still-air box and agar plates which are extremely sensitive to airborne contamination. If you start with the pre-sterilised uncle ben's bags and then transfer those to nutrient-poor bulk substrate like coconut coir (or straw for oysters), your sterility requirements are washing your hands and heating a needle. If you upgrade to a pressure cooker you can do about 5 colonies in an instant pot for a quarter of the price of an uncle ben's bag.