Windows 7 Pre-Order Offer: Home Premium Upgrade for $49 Professional Upgrade for $99 The offer ran from June 26, 2009 and continued while supplies lasted or until July 11, 2009, whichever came first.
These are estimated retail prices (US Dollars) for upgrade versions: Windows 7 Home Premium: $119.99 Windows 7 Professional: $199.99 Windows 7 Ultimate: $219.99
Estimated retail prices for the full packaged retail versions: Windows 7 Home Premium: $199.99 Windows 7 Professional: $299.99 Windows 7 Ultimate: $319.99
Note: Microsoft's states that Windows XP users will need to do a clean install. Also going from any 32bit version of Windows to a 64-bit version of Windows 7 will also require a clean install. "Microsoft designed Windows 7 Upgrade media for Windows Vista. A customer with Windows XP can purchase Windows 7 Upgrade media but must back up their files, clean install, and then reinstall their applications."
However I have found a path from Windows XP to Windows 7: (that may work for some XP users): "In-Place Upgrade Windows XP to Windows 7" http://www.pagestart.com/upgradexptowindows7.html (This article will be updated as more information becomes available)