Hi Jithin Prasanna,
Here is the limitation for Azure Backup, is in the support matrix web page: (https://video2.skills-academy.com/en-us/azure/backup/backup-support-matrix)
On the other hand there aren't limits to the total amount of data you can back up to the vault besides:
Maximum size of an individual data source is 54,400 GB. This limit doesn't apply to Azure VM backups. No limits apply to the total amount of data you can back up to the vault.
For instance on pricing page if you have 1.2 TB of data in one instance, then the cost would be $30 plus storage consumed. (https://azure.microsoft.com/en-us/pricing/details/backup/)
Let me know if this help that you are looking for.
Luis,