I’m planning an application that will use services across Azure, AWS, and Google Cloud. The architecture is still flexible, so I’m trying to understand whether cross-cloud traffic could become a significant part of the monthly bill.

How do you estimate cross-cloud data transfer costs before deployment? I’m especially interested in what to include beyond basic outbound bandwidth—for example, regional traffic, managed-service calls, and repeated data synchronization. If you’ve done this for a real workload, what usage assumptions or cost calculators gave you a useful estimate?