$3.3 Trillion

$3.3 Trillion | New York Times

An excerpt: "Al Qaeda spent roughly half a million dollars to destroy the World Trade Center and cripple the Pentagon. What has been the cost to the United States? In a survey of estimates by The New York Times, the answer is $3.3 trillion, or about $7 million for every dollar Al Qaeda spent planning and executing the attacks. While not all of the costs have been borne by the government — and some are still to come — this total equals one-fifth of the current national debt. All figures are shown in today’s dollars."

Another link that talks about the opportunity cost that America has squandered: The Price Of Lost Chances | New York Times

An excerpt: "Less than a trillion dollars of the $3.3 trillion was for direct responses — including toppling the Taliban. But what if at least some of the remaining $2 trillion plus had been spent on other, longer-range threats to American national security? Rebuilding a broken education system? Finding more imaginative ways to compete with China? Reducing the national debt? Or delivering on promises, by President George W. Bush and Secretary of State Hillary Rodham Clinton alike, for “Marshall plans” to rebuild societies at risk of letting the next Al Qaeda flourish?"