Hello.
I attach several links about ESXi free backup
Previously there was no backup software available for esxu free, but I see that now there are several options, I have not tried any of them but they seem interesting.
https://www.iperiusbackup.net/en/backup-esxi-and-vsphere-free-hypervisor/
https://www.unitrends.com/blog/free-esxi-backup-for-vmware
https://33hops.com/xsibackup-vmware-esxi-backup.html
About the normal VMware vShpere licenses are perpetual. what expires is the S&S Subscription and Support contract.
The licenses are always sold together with an S&S contract, that contract can have a duration of one, three or more years.
In the S&S contract the Subscription is the right to patches and new versions of VMware vSphere within the duration of the contract.
In the S&S contract the Support is the right to open cases with VMware for resolution, it has different parameters such as schedules, response time and more within the duration of the contract.
The kits include vcenter Server and ESXi host in different formats and variants.
Currently there are also licenses available for a certain time that is to say these licenses if they expire.
Attached link about licenses
https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/products/vsphere/vmware-vsphere-pricing-whitepaper.pdf