Engadget posted a story that Microsoft has announced the Windows 8 upgrade pricing for existing PC users

Microsoft has already detailed the Windows 8 upgrade route for those buying a new computer, and it's now finally confirmed what everyone else will be paying when they upgrade their existing PC. Those running Windows XP, Windows Vista, or Windows 7 will able to download a Windows 8 Pro upgrade for just $39.99. That's a far cry from the company's earlier upgrade prices, which as recently as Windows 7 ran $50 and $99 for Home Premium and Pro upgrades, respectively. You will have to pay a bit more if you want packaged DVD version of the upgrade, though, with it running $69.99 at retail -- it also sounds like both of those prices will be going up when the promotion ends on January 31st of next year.

  Microsoft announces $39.99 Windows 8 Pro upgrade offer for most Windows users