The Google Managed Prometheus says that they cost $0.2 per million samples. However, in pricing examples they say:
Scenario 1: You have 100 containers, each writing 1,000 scalar times series.
Variant A: If each time series is written every 15 seconds (1 sample/15s), then the number of samples written per month is 17,420,000,000 (175,200 samples/month * 1,000 time series * 100 containers), or 17.42 million.
But 17,420,000,000 is 17.42 billion. So in that example, the price should be $3600, not $3.60, which is a pretty big difference to a pocket.
