This write-up from Prezi Engineering explains how multi-AZ deployments can lead to surprisingly high data transfer costs. It documents their journey of migrating from a costly self-hosted Prometheus setup to a more efficient monitoring solution to save on their cloud budget.
https://engineering.prezi.com/how-using-availability-zones-can-eat-up-your-budget-our-journey-from-prometheus-to-be8a816f7efe