What are the hidden costs to consider while budgeting for Prometheus?

Even though Prometheus itself is open source and free to download, there are hidden costs you’ll want to budget for: paying for the infrastructure and storage to host/scale it, especially if you keep long-term metrics or run in big environments; the staff time and expertise needed to maintain, scale, and troubleshoot your setup; possible managed service fees if you choose a cloud provider or vendor; and extra costs for backup, long-term storage solutions (like Thanos/Cortex), alerting/visualization tools, and operational overhead that come with DIY deployments rather than a managed observability stack.