What they did was, 1.6 Trillion / (300 million people in the US / 4 people per family) = $20,900 (for 7 years)

But this figure is not annual cost, first of all.

It says during the year 2002-2008, and it's not even 2008, but that must be an estimation, so I'd say it's the cost for 7 years, so that's roughly $3,000 per year for average family.

And, $20,900 is assuming all the money comes from U.S. federal tax or what?

Bush admin collected money from Japan, Uganda, etc.. so we should exclude that from $1.6T too..

And $ collected from people who drive BMW will be lot higher than the average, of course...