Cheapest alternative is to buy the small business version of Windows. It comes with one copy of the windows required but 3 licenses. It costs less than buying individual retail copies
Those sellers with high ratings on Bonanza etc are also selling other legit products, so pump any ratings. When selling you a key, its a generated/illegal/stolen or unlicensed key that will actually work. Until you happen to get flagged by Microsoft a few months from now and Windows gets microcoded in the next automatic update, basically shutting you down. By that time you've posted your 5 stars for fast shipping, great price etc and Bonanza has kept no record of your purchase. So even if they get a slap on the wrist, you are now liable under software...