additional cost for dataset storage

Hi. When you are using Power Bi PRO licenses at a shared workspace there isn't additional costs. When you purchase dedicated capacity and use it in a workspace, it depends. Power Bi Embedded and Power Bi Premium (that can't be bought now) didn't have any addition cost for storage. On the other hand, Fabric has additional cost for using a storage like Lakehouse or Datawarehouse. You can find the pricing of storage at the web:

https://azure.microsoft.com/en-us/pricing/details/microsoft-fabric/

I hope that helps