AWS Cost and Usage Reports

I would highly recommend using Cost Explorer to get RI utilization and coverage. The result could be exported as a CSV for further processing. Please refer to https://docs.aws.amazon.com/whitepapers/latest/cost-optimization-reservation-models/aws-cost-explorer.html for more details.

Meanwhile, if you would be able to query Cost and Usage Reports using Amazon Athena, there are some reference queries available in https://www.wellarchitectedlabs.com/cost/300_labs/300_cur_queries/, specifically in Compute and Cost Optimization sections.