What makes the war on terror unique is that it is being fought to defend Americans in the United States. There were few Americans killed at home during World War II, Korea, or Vietnam. Moreover, those wars were fought against organized overseas foes. While the Cold War saw Americans menaced by Russian ballistic missiles, none of them were ever used. The war on terror gets more complicated because many more Americans disagree on exactly who the enemy is, and how the war should be fought. Thus the loud arguments over strategy and tactics.
But the war on terror is not going to break the bank, or come anywhere close to it. While World War II defense spending gobbled up 36.5 percent of GDP in 1944, Korea grabbed 13.7 percent in 1953, and Vietnam got 8.7 percent, today, total defense spending takes less than four percent. Casualties among the troops are a lot lower as well, as is the number of people in uniform. The only thing thats gone up is the number of American civilians killed. That, and fear of more of more attacks, makes it a war in most people's minds. But, by historical standards, defense spending is hardly at war time levels.
Whats the war in Iraq costing, compared to earlier wars? Currently, the war in Iraq is costing some $59 billion a year, which comes out to $200 per capita (for each American) just for Iraq. But the entire defense budget comes to $422 billion, which works out to $1,430 per capita. During the peak year of World War II spending, the war cost $900 billion (adjusting for inflation.) This came out to $6,475 per capita. The Korean War, in 1953, cost $500 billion (adjusting for inflation.) This came out to $3,145 per capita. The Vietnam War, in 1968, cost $922 billion (adjusting for inflation.) This came out to $4,610 per capita. For the entire war, per capita cost for World War II was about $18,000, for Korea about $5,600 and Vietnam about $8,000. The Korean and Vietnam wars were not as expensive as they could have been because Cold War spending was already high, and much of the military budget was simply moved from building defenses in Europe, to fighting in Vietnam or Korea. It was all in the service of fighting the "communist menace." The cost of the 1991 Gulf War was essentially zero, because nations that could not send a lot of troops (like Saudi Arabia and Japan) sent lots of money instead.