I do not have an HA setup BUT all of my proxmox vms are snapshot backuped by proxmox backup server every night to my home NAS and to my office NAS. You can use one of many storage providers. SSHFS also works. This is the cheapest and lowest administration solution I used till today. For production usage I would recommend 3-4 similar speced 28€ machines and run a replicated proxmox cluster or ceph proxmox cluster.