Hi @VOIROL CHRISTIAN ,
if an Azure Virtual Machine is in state Stopped (deallocated)
there are no charges for the compute part of the Azure VM . Just start the VM for your required work and stop/deallocate the VM if not needed anymore.
For all the disks of an Azure VM the costs are charged as long as the disk exists, no matter the VM is running or deallocated. This is because the disk will use resources in the Azure datacenter.
Your best option is to convert the Azure disks into Standard HDD
and the smallest size that fits your needs. It's possible to convert the disk type (Standard HDD, Standard SSD or Premium SSD) forth and back without an issue.
On the other hand you can remove/delete the data disks completely if the VM is not in use and create new data disks if required. This way you are only charged for the OS disk of the Azure VM during the "inactive" period. For instance 128 GB Standard HDD in a Azure US region about 6US$ per month.
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you) Regards
Andreas Baumgarten