The decade old, open source, self hosted, debug it yourself standard for monitoring is collectd+graphite+grafana.
The equivalent easy to setup and use, with ALL the features working out of the box, SaaS standard is https://www.datadoghq.com/ or potentially Google Stack driver if you are on Google Cloud.
The thread you are linking to is a complete joke. The guy didn't see that the pricing was per host, even though it's written in big letters. His whole series of rant is ridiculous.
Stack Driver is a Google Cloud service, you need a Google account with billing to use it. It can gather metrics from hundreds of vendors, including AWS and Azure.
The equivalent easy to setup and use, with ALL the features working out of the box, SaaS standard is https://www.datadoghq.com/ or potentially Google Stack driver if you are on Google Cloud.