Hello @matjung
Thank you for sharing this question on this community space.
I would like to gather the next articles which fits into your previous statement the one you were describing previously related to 3rd party VM OS, billing and OS support.... So please direct yourself down below:
https://azure.microsoft.com/en-us/pricing/calculator/
https://learn.microsoft.com/en-us/azure/virtual-machines/sizes
https://learn.microsoft.com/en-us/azure/marketplace/marketplace-virtual-machines
https://learn.microsoft.com/en-us/azure/marketplace/plans-pricing
Moreover, I would say that if you want to pay less money for it, you can choose the option reserved instance for Virtual machines. Also, you will be charge for the usage like storage, networking and so on...
If you can deallocate the VM that is being used in order to decrease the billing charges and program policies to shut down the VM as well.
I hope you can find this useful to address your concern.
Looking forward to your feedback,
Cheers,
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