Linux is very cheap compared to Windows. Microsoft allows a single copy of Windows to be used on only one computer. You can buy a Linux book and get the operating system included with the book for free. You can also download Linux for free from each of the Linux vendors (assuming your Internet connection is fast enough for a 600 MB file and you have a CD burner) or from
www.linuxiso.org.Both these options however, come without technical support.
After the initial cost (or lack thereof) of obtaining software, there is the ongoing cost of its care and feeding.
I don't know if there will ever be an objective measure of the ongoing care and feeding costs for Linux vs. Windows. If there were however, it would have to consider:
Dealing with bugs in the operating system
Dealing with bugs in application software
Dealing with viruses, worms, Spyware, etc. (big advantage to Linux here)
Dealing with software upgrades to new versions (both the OS and applications)