Hi @Catija, we are out till the end of next week on our yearly meetup.
I alerted the right people who can offer a response here, but it will likely take a bit.
Creating pricing tiers for a product is part art, part science, and part guessing.
It is not all based on “what it costs us to host” instead, we try to create the tiers to match “types” of customers and provide the right value at the right price point. Hobbyist communities with low traffic tend to need a lot less moderation; businesses tend to need more. It is worth noting that at the enterprise level, we don’t tend to worry that much about admin counts, though I would say too many bosses can be an actual pathology in community.