IMHO, spores to birdseed to pasteurized used coffee grounds and coir is the most cost effective way by far.
Just spawn the colonized birdseed to the coir/coffee substrate at a ratio of about 1-10, and fill the bottom 3-4 inches of a rubbermaid container with them. Drill a few holes in the top for light, and a few small (1/8 ") holes on the sides about 2 inches above the top of the substrate. With that and opening up and fanning once a day, you will have all the air exchange you need. Misting is not required if H20 content is correct at the time of spawning.