@Brian Welcome to Microsoft Q&A Forum, Thank you for posting your query here!
There are no additional charges for soft delete. It's just that you will continue incurring cost for the deleted data till the soft delete period ends.
All soft-deleted data is billed at the same rate as active data. You won't be charged for data that is permanently deleted after the retention period elapses.
When you enable soft delete, Microsoft recommends using a short retention period to better understand how the feature will affect your bill. The minimum recommended retention period is seven days.
Enabling soft delete for frequently overwritten data may result in increased storage capacity charges and increased latency when listing blobs. You can mitigate this additional cost and latency by storing the frequently overwritten data in a separate storage account where soft delete is disabled.
You aren't billed for transactions related to the automatic generation of snapshots or versions when a blob is overwritten or deleted. You're billed for calls to the Undelete Blob operation at the transaction rate for write operations.
For more information on pricing for Blob Storage, see the Blob Storage pricing page.
Soft delete for Blob storage - Pricing and billing
Soft delete and versioning charges the capacity being used by soft deleted blobs, or versions.
The exact cost depends on how often your data is modified or deleted. If you didn’t modify anything or delete anything. There is no extra cost. If all 100GB is deleted, then you are paying for the 100GB for 30 days of the soft delete.
If you still have any questions, I recommend to please contact Billing and Subscription team would be the best to provide more insight and guidance on this scenario: https://azure.microsoft.com/en-us/support/options/ It's free and best choice for your scenario, where they can provide detailed information on your scenario based on your region and requirements
Please let us know if you have any further queries. I’m happy to assist you further.
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