As with previous releases it looks as Microsoft will once again be offering an upgrade offer for those purchasing a Windows 7 computer in the months leading up to the release of Windows 8. And the rumored cost for that upgrade is just $14.99.
According to CNET, Microsoft is to offer a Windows 8 upgrade promotion over the next few months. Anyone buying a machine running Windows 7 Home Basic or higher will be given a coupon allowing them to upgrade to Windows 8 Pro after it hits retail. The offer is expected to begin around the beginning of June and, according to a further report on Windows SuperSite, cost an extra $14.99. So not quite but almost free.
This date is expected to coincide with the unveiling of the Windows 8 Release Candidate. It also means Windows 8 remains on target to hit retail around October.
Source
What will come in Windows 8 Pro?