@Mirella Pellizzon Petruci Welcome to Microsoft Q&A forums.
The cost associated with Outbound Data Transfer (Internet Egress) is minimal.
Unless you are transferring Terabytes of data it is not going to be significant.
Internet Egress of 5GB/Month is free per subscription.
Beyond that, the charges are $0.08 per GB (in North America and Europe).
For a complete list of charges by region, please check the Internet Egress section on this page.
If an answer is helpful, please "Accept answer" or "Up-Vote" which might help other community members reading this thread.
And if you have further questions or issues, please let us know.