The operational cost of growing marijuana, even indoors with pretty high-powered lights, is actually extremely low. You can make it expensive buying fancy nutrients and gimmicky hydro systems but when I was growing for the black market before legalization, me and every other grower I knew (we were legion) poured reasonably-priced nutrients into cheap pots under cheap lights and grew dank buds ferda.
Now (here in Canada anyways), a few giant corporations, in theory, do all the growing for the legit market, and need to handle a lot of large-scale problems, like big central grow ops requiring 1.21jigawatts instead of a bunch of houses using a bit of extra hydro each, security, pilferage, all the big problems of scale. These are problems of growing at scale, though, not problems inherent to growing weed.
We didn't have the problems of scale as a community of indepdendent growers. We had other problems: cops, filtering the smell so as to be good neighbours, larger ops had to deal with moisture, the reputation brought on by low-rent gangster scumbags who rent houses, setup and then threaten the landlord. We had the problems of an unregulated market, and the quality of our product as well as knowing a dealer determined our success, but basically anyone with basic competence and the ability to keep their mouths shut (ie. the barest of street smarts) could make an okay living back then.
I would say that Silo/Fedi is going to have a similar dynamic, minus the cops. Moderation happens by volunteers because people want to have a voice in determining what rules make the most sense for the communities they participate in, it's a non-issue in either world. Smaller instances will have smaller moderation loads, larger instances will either get supported by their users (money, work, whichever) or break up, or whatever, but it's going to settle into a congenial equilibrium in which the community of operators and users all look out for each other. We have seen the alternative, and we do not care for it, so we are going to put in the effort.