Does anyone have an idea about the infrastructure requirements and the cost of running an instance with the size of mastodon.technology?
I think they're the largest managed hosting provider in this space. Obviously they are charging a premium compared to deploying it all yourself, but I think the prices are fair, and the plans give you a pretty good idea of the resources required.
No offense to the other admin, but $200/mo for 50 active users is way too high. A Kubernetes cluster for 50 users is obvious overkill IMO. Maybe you did it that way for the learning aspect, which is fine. You should be able to host 50 active users for a 10th of that cost though. You can easily do it on a single VPS.