Thank you for the feedback. The management fee is per cluster. You are not billed for replicated control planes. You can use the pricing calculator at https://cloud.google.com/products/calculator#tab=container to model pricing, but it should work out to $73/mo regardless of nodes or cluster size (again, because it's charged per-cluster).
There's also one completely free zonal cluster for hobbyist projects.
There's also one completely free zonal cluster for hobbyist projects.