Here's a comprehensive summary of the prices for the versions of Microsoft latest OS, Windows 8 (Pro versions of the OS or download pack).
Windows 8 Pro, is available in 32 and 64-bit and is intended for both a personal and professional use. The Pro version combines all the features of the OS. Among others: data encryption technology, a virtualization ecosystem (creation and management of virtual machines), a toolbox for advanced management of the system, and various networking functions.
Windows 7 users: upgrading to Windows 8:
Users who purchased a PC with Windows 7 "between June 2, 2012 and January 31, 2013 may receive a special offer, they can upgrade to Windows 8 Pro for $14.99. This offer is not intended for commercial enterprises.
Windows 8 Pro will only work on devices powered by the Intel x86 processor family (eg Intel, Pentium, etc..), The Windows RT version is available for ARM devices, which consists primarily of touch pads.