Disk latency, and one's aversion to it, is IMHO the only way Hetzner costs can run up on you. You want to keep the database on local disk, and not their very slow attached Volumes (Hetzner EBS). In short, you can have relatively light work-loads that will be on sort of expensive VMs because you need 500GB, or more, of local disk. 1TB local disk is the biggest VM they offer in the US. 300 EUR a month.