according to MS there is a Azure Service bus component to on-prem data gateway , however when you install the Azure component no service bus resource created. we need to understand the impact on pricing i.e. is the price of service bus hidden within Azure on prem data gateway ? there is no pricing guidelines for Azure On premise gateway
There is not a licensing cost for the data gateway and data flowing into Azure is free. You pay egress costs which can be calculated using https://azure.microsoft.com/en-us/pricing/details/bandwidth/