Cloud data transfer costs represent 10-18% of total cloud spending and are among the most overlooked yet impactful drivers of cloud bills. Ingress (data moving into cloud infrastructure) is typically free across all major providers, while egress (data leaving cloud infrastructure) incurs charges that vary significantly by destination, volume, and provider. Understanding the nuanced pricing models—from inter-AZ charges ($0.01/GB) to internet egress fees ($0.09-$0.12/GB) to cross-region transfers—is essential for cost-effective cloud architecture. The key insight: architectural decisions made early determine whether data transfer becomes a minor line item or a budget-crushing 15% tax on every workload.