Help finding a monitoring system

Hi, I've been looking for a simple agent/server monitoring system that fits my particular bill. I want the agent to monitor the return of several APIs, commands, etc and send the data to the main server that will send me alerts. There won't be any direct access between agent and server so the data has to be pushed through API via internet or something similar.

What I've tried:
* check_mk: it's kind of a freemium experience plus push is paid.
* zabbix: used it for years but configuring is a pain
* grafana+prometheus+whatever: overkill

Also couldn't find anything like this on the awesome-selfhosted repos, some help here please.