There are basically three different ways you can handle the bandwidth billing from Microsoft.

Metered model:

The most straight forward one would be metered model where you “pay as you go” per GB of egress traffic. The price ranges from 0,02 € to about 0,11 € depending on the Network Zone. An overview of all onramp locations and the matching zone can be found here: https://docs.microsoft.com/en-us/azure/expressroute/expressroute-locations-providers#partners

Unlimited model:

As the name suggests the whole egress traffic is included here. Depending on which SKU you are using (Standard or Premium) also inside the whole Microsoft backbone. With the standard SKU all traffic inside the geopolitical region is included, for example Europe, and with the Premium SKU even worldwide traffic is included. But traffic from the Global Reach Add-on is always billed separately. Please calculate if it makes sense for you to use this option, because it can become very expensive. You can do this with the Azure cost calculation tool https://azure.microsoft.com/en-us/pricing/calculator/

If you upgrade a circuit from metered to unlimited you cannot reverse to metered anymore without reprovisioning the whole circuit.

Local Model:

The local model works almost the same as the unlimited option but with some slight differences which are important to know. The first difference is, it is only available for connections 1Gbps or higher. But the most important thing to know is that you can only connect vNETs from the same datacenter region. For example if you have the onramp-location Frankfurt it is not possible to connect networks from other regions than “Germany West Central”.