I run OSS Grafana with Loki, Prometheus, and Tempo. I use an Alloy sidecar taking in OTEL and scraping logs.feom my Go services and selfhost the stack. Once you need to scale it gets a bit more complicated but it's all still OSS.

The biggest challenge I have is that each data source needs it's own query language, which DD and the like don't. That's why at my day job they went with DD despite the costs. Still OTEL but the querying is the same. We are also looking at Dash0 but for all of my personal and consulting jobs, OSS LGTM/P works good for me.