@Gerard Blackburns​ :

Calculating the cost or billing for Azure SQL Server instances involves considering the Azure SQL Database Unit (DBU) pricing model. DBUs are the unit of measure for the consumption of Azure SQL Database resources. To calculate the cost, you need to consider the following factors:

1. Database Service Tier
2. vCore-based or DTU-based Pricing
3. Number of vCores or DTUs
4. Region and Availability Zone
5. Storage Cost
6. Managed Instance or Single Database

To get precise pricing information based on your specific requirements and configuration, you can use the Azure Pricing Calculator (https://azure.microsoft.com/pricing/calculator/)