What is so expensive?

I was reading a CNN.com article about the civilian plane that wandered into forbiden airspace near the White House, causing an evacuation. F-16s escorted the plan to a nearby airport and forced it to land.

Here’s a quote from the article: According to NORAD — the North American Aerospace Defense Command — it costs between $30,000 and $50,000 just to scramble a single fighter jet.

So … my question is simply this: Where does all that money go? Mostly fuel, I’m guessing? How much does it cost just to fill the tanks in one fighter?

–Gavin.