This question has come up many times, so posting about it here.
Microsoft does not charge for ingress or egress with Office 365, all data transfers are covered under their per user licenses.
Azure only comes into play when doing restores to SharePoint Online, assuming the client is running every thing on-prem (which most don't but for the sake of this part of the blog post let's assume that). The data being restored is written to an Azure storage account, then the SPO Migration API is called, which only supports putting data from Azure. After the restore is done the data in Azure is deleted. There is no ingress charge for data into Azure, but there is egress and storage charges.
Now if a customer is running Commvault in Azure to backup O365, to backup\ingest the data there are no charges. But if they are restoring data to Office 365, on-premises, or outside of their Azure tenant then there might be egress charges. If they are using Metallic, this is all covered under their per-user subscription at no additional cost.
For data egress the 1st 5GB/month are free, so if the data being restored is less than 5GB in a month there is no charge for network transfers. After 5GB it’s $0.087/GB or cheaper: https://azure.microsoft.com/en-us/pricing/details/bandwidth/
As for Azure storage, the data is there for the length of the restore job time. So again it depends on the size of the data being restored per month, but in general with many GBs being restored the storage charges would still be WELL under $1.
Pricing for Azure storage is here: https://azure.microsoft.com/en-us/pricing/details/storage/. For Hot storage the rate is $0.0184/GB per month for the 1st 50 TB. So if they had 100 GB being restored in a month that was sitting on storage for a total of 1 hour, this would come out to $0.003 (or under a penny).