Q. Are there any data charges if using VNET peering?
A. VNET peering enables two virtual networks in the same region to be connected via the Azure backbone without having to use gateways. Ordinarily only egress traffic to a region is billed however the Azure pricing page is the best resource for authoritative information on pricing and networking information can be found at https://azure.microsoft.com/en-us/pricing/details/virtual-network/. The page shows that when using VNET peering traffic is charged for ingress and egress at both ends of the peered networks. At time of writing this charge is $0.01 per GB of data and remember that it is charged at both ends so where data is egress to one network it is ingress to the other and therefore billed twice.