How much effort does it take to run a self-hosted open-source monitoring stack?
More than most small teams expect: installation is the easy part, keeping it useful is the ongoing work. Plan for a dedicated server with enough storage for logs, regular software and rule updates, disk and performance monitoring of the stack itself, tuning to reduce noise, and time every day to read alerts. When something breaks, such as a full disk or a failed update, detection stops silently until someone notices. Document the setup so that it survives the person who built it leaving. Estimate the hours honestly and price them at your internal rate before calling the stack free. If the hours are not there, choose a tool that runs without upkeep and spend the saved time on investigating alerts instead.