CloudHealth does not charge any additional fees for agent usage.
The only cost implications would relate to the traffic/utilization costs as the agent itself does upload metrics payloads to our API server but the cost of this should be extremely minimal. This means the only cost would be associated to the API calls made between the EC2 instance and CloudHealth. There would not be any line item in the DBR specific to the agent. It would roll up under Network In/Out and would be relative to the amount of data uploaded by the Agent and there will be a slight increase in traffic between AWS and our platform that may increase your Instance/Network costs on the AWS side slightly.
It would be about 1 MB per day per instance.
AWS Pricing table for data uploaded:
First 1 GB / month $0.00 per GB
Up to 10 TB / month $0.09 per GB
Next 40 TB / month $0.085 per GB
In terms of the number of API calls, CloudHealth makes about 2k API calls per instance per hour.
If you are installing the agent to allow more detailed Rightsizing, the savings made by rightsizing should be many magnitudes higher than the small costs related to uploading metrics.