Thanks for the solution. I’m thinking about this in a whole month. And you are right Vultr is the cheapest VPS I found so far
Have you tried OpenVPN Cloud? or AWS free tier + OpenVPN
Just FYI - Mikrotik ROS can be installed on x86_64 hardware, and I mean virtual machine. What I am trying to say that you can setup RouterOS on VPS, I’ve done it in Linode. Monthly cost of your instance + single purchase of ROS licence ($40 for L4) and you can setup VPN in your familiar ROS environment. 
But using Linux distro, like Debian, you can setup your own ipsec/ike2 VPN server using Strongswan, but it would be significantly harder if you’ve never done it before…
And if you decide to use Mikrotik ROS, you can follow the same guide I’ve shared few comments up. Basically you can end up having a public IP for your router which is behind NAT. EoIP on top of IPSEC/IKE2. P.S. Don’t go for OpenVPN - it’s slow.