I can't hit four nines reliably with single VPS platforms on my typical workloads, I need load balancers and redundant app servers. I could quite likely hit three nines using single VPSes. But if a client wants 99.9% SLAs, they'll be paying for HA and I'll deploy redundant ec2 instances, multi region RDS, and an ELB. And charge them 3 or 4 times what the OP is spending for it. (And I'll almost always deliver 99.99% availability.)

For my stuff or friends or people I'm doing cost saving favours for, I'll explain how much extra it costs to guarantee less then an hour of downtime a month, the realistic expectations and historical experience of how much downtime an non-HA platform might have in their use case, and often choose along with them a single VPS (or even dirt cheap cpanel hosting) while understanding and accepting the risks associated with saving upwards of a couple of hundred bucks per month.