And it seems to me he comes out in the black.

Costs: A few bucks for flight training, some planning, and a few guys willing to die for the cause.

Benefits (from OBL's perspective): thousands of Americans dead, one symbol of US destroyed and one severely damaged, billions of dollars in direct and indirect damage, fear struck in the hearts of almost all Americans, redirection of attention to Saddam, further billions of dollars spent on wars in Afghanistan, Iraq, and around the world, restrictions on American's fredoms, international schisms, a refocussing of US attention away from it's real problems of the economy, etc - and Osama still on the loose (absent any evidence to the contrary).

Sounds to me like about the biggest payoff in history.