I recently wiped a windows 8 machine and installed Ubuntu. I now need to sell this machine, and the people I want to sell it to would like it to be running windows 8 again. I've been looking around online, and I was under the impression that I could simply order a recovery disk or a re-install disk or something similar. But I'm getting a lot of different answers. What is the right (legal, cheap, in that order) way to do this?