Windows 8 upgrade editions will be sold as follows after jan 31st 2013:
The Windows 8 Pro upgrade edition will be available online and at retail for $199.99 MSRP (U.S.).
The Windows 8 upgrade edition will be available online and at retail for $119.99 MSRP (U.S.).
The Windows 8 Pro Pack will cost $99.99 MSRP (U.S.).
The Windows 8 Media Center Pack will cost $9.99 MSRP (U.S.).
Source: