Hi @sakuraime , welcome to Microsoft Q&A forum.
The cost implications depend on max storage we configure while provisioning the database. Please check the below screenshot:
Also if we keep on changing the slider as shown in below screenshot, the per month cost changes accordingly. This storage can be changed even after provisioning the database:
Storage Size 200 GB:
Storage Size 100 GB:
Please let us know if this helps or else we can discuss further.
If answer helps, please mark it 'Accept Answer'