Microsoft is now selling the full retail version of windows 8 for 39.99. The normal price is 249$.
This is not the upgrade version, This is the full retail that finally let you legally install windows 8 on any computer.
EDIT: It look like it may be some website error from Microsoft, Some Tech site wrote them to know if it's an error or the retail. Will have more new in a couple of minutes.
EDIT 2: It look like it's just a microsoft problem, this is the upgrade, they change the normal price.
Find it here