https://d3g5gsiof5omrk.cloudfront.net/nixos/unstable/nixos-18.03pre116572.9824ca6975/nixos-minimal-18.03pre116572.9824ca6975-x86_64-linux.iso
NOTE: first fork https://github.com/somlor/nixos-vultr-bootstrap and edit ssh key with your public ssh key. Now in Vultr console:
$ nix-env -iA nixos.gitMinimal
$ git clone https://github.com/your-username/nixos-vultr-bootstrap
$ cd nixos-vultr-bootstrap
$ ./bootstrap.sh
$ reboot
From your own machine:
$ ssh nixos@vultr-ip-address