Still, it's useful to have some ammunition for the other side, and this report about a migration carried out in Bristol provides that. As the Guardian summarises:
Bristol calculated a five-year total cost of ownership of £670,010 for StarOffice, compared with £1,706,684 for Microsoft Office. This was despite budgeting half as much in implementation and support costs for Microsoft because many users were already on its systems.
The difference may turn out to be even greater, says IT strategy team leader Gavin Beckett. "We discovered that things were simpler than we thought they'd be," he says of the switch. "We always argued that a lot of the risk was perceived risk, rather than real risk."
Update: No TCOs here, happily, but 35,000 users have been moved to OpenOffice.org in Brazil according to this story.