An Azure relational database service.
it would depend on a lot of factors. If they are provisioned single Azure SQL databases then they are billed per hour. If they are serverless then it's per second. You would see cost savings if they were deleted for a time here.
If you are using an elastic pool for all 4 databases then you won't see any cost saving.
https://learn.microsoft.com/en-us/azure/azure-sql/database/cost-management