I see that there is discussion on the page about having various browsers running in virtual machines.
A relatively cheap solution for this is VirtualBox, an open source project under GPLv2 for virtualization run by Oracle. This is an easy way to create VMs for Windows and various flavors of Linux (OS X is forbidden by Apple licensing requirements).
Some groups have been using VirtualBox in conjunction with Vagrant, which can deploy VirtualBox VMs through command line and/or script to set up test environments easily and then to take them down again.
I'm told that there may be licensing restrictions on using more than a set body of VirtualBox instances from Oracle but it isn't clear to me what the strictures might be and there are no docs about it on the website that I've seen.