I'm only interested in a liscensed full retail version.
You only have two options currently available. You can get the upgrade version or the OEM system builder version. The upgrade can be installed on a bare drive so it's by far the cheaper of the two options.
1. Run the registry editor (regedit)
2. Find the following key: HKEY_LOCAL_MACHINE \ SOFTWARE \ Microsoft \ windows \ Currentversion \ Setup \ OOBE
3. Change the value for ' MediaBootInstall ' from 1 to 0
4. Open an elevated command prompt (run as admin)
5. Run the following command: slmgr -rearm