As the other thread from today brought up the infrastructure cost question for a Reddit alternative, here is a link to this question to Lemmy admins: https://lemm.ee/post/41577902

Summary of the answers:

• lowest number so far: lemmy.ml with 0.03€ per user per month
• a few others (feddit.uk, lemmy.zip) have around 0.11$ per user per month
• some instances are running on infrastructure that the admins would be anyway, so it's virtually "free"

Most of the instances costs are paid using donations. They regularly post financial updates such as this one: https://lemm.ee/post/41235568

Obviously there is a sweet stop where you can minimize the cost by having the maximum number of users on a fixed infrastructure cost.

If you want to have a look at the number of monthly active user (the "MAU" column): https://fedidb.org/software/lemmy/

If people want to give Lemmy a try, https://lemm.ee is a good choice to start.

You can use an app from https://www.lemmyapps.com (including Sync, Boost and Voyager, an Apollo clone)