Which RDS storage option meets these requirements MOST cost-effectively?

Explanations:

General Purpose SSD (gp3) provides a balance of price and performance, offering cost-effective storage for workloads like nightly batch processing that do not require extremely high IOPS. It is suitable for most workloads, including large database migrations, and can scale in both performance and capacity without high costs.

Provisioned IOPS storage (io2) is designed for high-performance needs, such as transactional systems requiring high IOPS, and would be overkill for batch processing. It is more expensive than General Purpose SSD and unnecessary for the described workload.

Magnetic storage (standard) is outdated and not recommended for modern workloads. It is much slower and offers lower performance compared to SSD-based options. It also has higher risk of failure, making it unsuitable for production database migrations.

Throughput Optimized HDD (st1) is intended for large, sequentially accessed data like data warehousing or big data applications, which doesn’t fit the needs of an SQL Server database primarily used for batch processing. Additionally, HDD-based storage options are slower and less reliable compared to SSD options.