I've tried to scale down a single fruiting medium to 100-200g, and it keeps failing time after time: at best, I get small needle-sized fruiting bodies (hypsizygus tessulatus, post picture) or primordia and then small malformed underdeveloped fruiting bodies (pleurotus eryngii, inline picture). Then development just stops. Medium is enriched (sugar) alder chips, contamination starts developing long after growth is stalled. Is it really scale problem? What's the reasonably smallest batch size?
To throw out some easy options, in a humid chamber, a plain cardboard box roughly the same volume as those jars would do great, especially with a few 1/4” holes added.
A closed 12-ct paper egg carton with a few holes where you want fruiting would also do nicely, but that’s probably right on the line of minimum growth medium necessary for decent fruit.
And if you get bored of the scaling-down experiment, you’d be well served with some 3-gal food-grade buckets with a few 1” holes. Still plastic — but readily available, indefinitely reusable, and should fit your chamber nicely!
Yeah, I'm thinking in direction of edible (for mushroom) containers; maybe some cardboard origami, or simple wood plank box; I'm even thinking to try casting linoleum pots on woven jute. It must be doable, why nobody does that now?
Definitely doable! I learned how to grow through a class hosted by my local myco society, and they made a point to show us oysters growing in + on all sorts of wacky things. Shoeboxes, laundry baskets, water-damaged homes, etc.
Just hard to beat the cost of plastic grow bags at scale :).