There was a recent email on the Linux kernel mailing list about the cost to reproduce Linux 2.6 from scratch. It used a standard model. With over 4 million lines,takes over 1300 person-years of effort. To finish in 8 years requires over 150 developers, for $175 million in salaries.
It bet if you added up the research and development expenses of open source companies, you would end up with a significant chunk of change.