ExpressRoute, multiple subscriptions, cost management
We are a company with an existing Azure subscription, which currently only hosts Sentinel and a few other random storage accounts, B2C tenants, key vaults, etc. for various purposes. All of this is in a single subscription. We currently run 100% of our compute infrastructure on premises.
In the near future, we'll be standing up ExpressRoute and migrating our test/dev VM infrastructure into Azure. I'm planning out how to structure all of these resources in Azure. It sounds like standing up a new subscription would be the recommended way to go for this new test/dev infrastructure. Then if we begin standing up some production workloads in the future, standing up another subscription for that, etc.
However, if we create our ExpressRoute in our existing current subscription, my understanding is that by having our compute resources in a different subscription, we'll be incurring additional network ingress/egress costs, whether that be from vNet peering or an ExpressRoute gateway from the second subscription. How are others managing this?
I'd love to go the multiple subscription route to keep resource organization and RBAC permissions clean, but this may be hard to justify in our case if this means incurring additional networking costs that could otherwise be avoided by just dumping everything into one subscription.