Which solution will meet these requirements MOST cost-effectively?

Explanations:

Amazon Redshift is a data warehousing service designed for analytics and complex queries rather than operational workloads. It does not provide immutable logs or cryptographic verification of changes, which are key requirements for the solution.

Amazon Neptune is a graph database service that is suitable for highly connected data but does not focus on providing immutable logs or cryptographic verification of changes. It is also not specifically designed for accounting records, making it less optimal for this use case.

Amazon Timestream is designed for time-series data and may not meet the specific requirements for accounting records, particularly in terms of immutability and cryptographic verification. It is not geared towards traditional relational data management.

Amazon Quantum Ledger Database (QLDB) is specifically designed for applications that require an immutable and cryptographically verifiable log of data changes. It provides a fully managed service with minimal operational support, making it the most suitable and cost-effective solution for migrating accounting records.