I think I would reiterate what David said, if data integrity is an issue, then I would very much advise PostgreSQL over MySQL.
MySQL really is a lightweight compared to Postgres.
The big problem with MySQL and the main reason data integrity is an issue is the complete lack of transaction support. This will be introduced with V4 but that is only available in alpha at the moment.
PostgreSQL on the other hand is a real built from the ground up transactional database server
But if you want the company supported line, (read Microsoft) the the only answer is not cheap, SQL Server.