If you're using Hyper-V, you get an unlimited number of guests if you've purchased Windows Server Enterprise Edition. Last I checked, it's not even that expensive of an upgrade.
Or just use Windows Datacetner Ed on your hypervisor. Most cloud providers have that as an option. It's like $200 a month and you can run as many VMs as your hardware will support.
I guess that at many places you'd just buy datacenter edition, but that's a bit too much for small businesses.