What should the solutions architect recommend to meet these requirements at the LOWEST cost?

Explanations:

While S3 batch operations can be used to manage object tags, this option does not directly address the requirement for deleting older versions after 2 years. Additionally, modifying tags does not automatically manage the lifecycle of versions; a lifecycle policy would be more appropriate for expiring objects.

This option meets the requirements effectively by using an S3 Lifecycle policy to transition older versions to S3 Glacier, which is a cost-effective storage solution for infrequently accessed data. The policy can then be configured to expire (delete) the objects after 2 years, ensuring compliance and cost efficiency.

Enabling S3 Event Notifications to send older objects to an Amazon SQS queue does not provide a method for deleting or managing the lifecycle of the object versions. This approach would add complexity without addressing the requirement to automatically delete objects after 2 years, making it an inefficient solution for cost management.

While replicating older object versions to a new bucket could allow for different lifecycle policies, this option adds unnecessary complexity and cost. Managing two buckets incurs additional storage costs and overhead, and it does not provide a more effective solution for the specified requirement of deleting objects after 2 years.