Watching a few courses right now and one of them is the AWS SysOp - Associate course.
I am at the episodes talking about metrics/monitoring etc. To get the RAM usage, you need to install perl, and use a script.
Couldn't this be done for every metric, and the data stored into a csv somewhere, which is then accesible. Basically, couldn't you just bypass the entire extra CloudWatch costs? Surely there is something open source out there.