Snapshots in RDS are your backups of your database tables and instances, and these snapshots can then be exported out of Amazon RDS, to Amazon S3.  You might want to do this perform analysis of the data held within your database using more specific tools, for example, Amazon Athena, which is an interactive query service that allows you to perform analysis on data that you have stored in Amazon S3 using a standard SQL.  

You could also use other services, such as Amazon SageMaker and Amazon Elastic Map Reduce (EMR), however, the point is, the data can be exported from your RDS database to S3 for further in-depth analysis as required.

Also, during an export of a snapshot, you can decide, through filtering, to simply export specific databases, tables, or even schemas.

The cost associated with performing snapshot exports are again based on a region by region basis.  The example here shows the costs for the Ireland Region when using MySQL and is based upon a cost per GB of snapshot

For additional security and protection of your exported data, you can encrypt the data using the Key Management Service (KMS).  As a result, additional KMS costs would be incurred depending on the KMS key selected.  For more information on the Key Management Service, please see our existing course here: https://cloudacademy.com/course/amazon-web-services-key-management-service-kms/

Also, you will also be charged costs associated with Amazon S3 for the storage and your PUT requests.  For more information on how Amazon S3 costs are calculated, please see our existing course here: https://cloudacademy.com/course/understanding-optimizing-costs-with-aws-storage-services/