Running modern full-fat Linux on anything sub-512MB isn't a great experience unless you're willing to do a lot of tweaking, or running specialized distros like alpine. If dropping the whole "vm" thing is an option, you can go much lower -- I've been running perfectly usable alpine lxc system containers on as low as 32MB -- though container-based vps kind of fell out of favor in the last couple years, probably due to the issues that come with not having your "own" kernel in "your" vps. Virtuozzo/openvz was everywhere back then, now it's pretty much all kvm/vmware/hyperv.