The Linux foundation has just published a study, telling us that Linux costs $10.8 billion. Or almost. They have tried to evaluate how much it would cost to develop a Linux distribution from scratch, taking Fedora 9 as an example. So it is not just Linux itself - the kernel is estimated to "cost" about $1.4 billion. This calculation is based on the average salary of a US software developer and the lines of code in the system. Apparently, that developer earns $75,662.08 a year, costing the company $97,604.08.
Obviously, there are a few problems with this approach - calculating, for instance, the cost of iterative development of the kernel. But it leads (or should lead) to a nice discussion about what open source software is worth, not what it did cost:
http://www.linuxfoundation.org/publications/estimatinglinux....