You're off by at least an order of magnitude there. I see estimates from $6 trillion[1] to $8 trillion[2] for the cost of the war on terror. Taking the high estimate and the 2001 population of 285 million (i.e. ignoring population growth since 2001) gives $28k per person, or $1400 per year over 20 years. Accounting for population growth and taking the lower cost estimate decreases the amount further.
