Depending on the number of metrics and API requests you call you could have enough with the free tier. After the free tier yes, you will be charged for the API requests you call. Example: GetMetricStatistics, ListMetrics, PutMetricData, GetDashboard, ListDashboards, PutDashboard and DeleteDashboards requests $0.01 per 1,000 requests.
You have some examples in the pricing link.
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