Cost for premium connector is 15$ per user who owns the flow. If you have dev, test, prod environments, then you'll need a premium account for each service account. Also you might need premium connection for developers and business owners. Just keep adding 15$ per each flow author/editor.
Now if your users trigger the flow from flow ui, then you'll also need licenses for each user running the flow I believe, because the flow contains premium connectors. But if a power app consumes flow and the users just use the power app you don't need to get licenses for your users.
My recommendation is to contact microsoft sales team to iron out all these things instead of relying on a forum.