You can use grafana which contains APM, logs, metrics and alerting with a free tier for tiny projects. But honestly if you get 10 requests, you likely don't need APM and if you need APM, you should be getting at least $50/mth from your service.
Or just host the grafana (or different) stack yourself.
Grafana sucks imo. Their UI is bad, it takes time to setup. It's very difficult to maintain it all together. There should be a free alternative. I'm surprised there is literally no free alternative to Datadog.