Last Friday, National Rifle Association CEO Wayne LaPierre suggested putting armed police officers in every school in America as a means of warding off the kind of tragedies as recently occurred in Newtown, Connecticut. “With all the foreign aid, with all the money in the federal budget, we can’t afford to put a police officer in every school?” he asked. “I call on Congress today to act immediately, to appropriate whatever is necessary to put armed police officers in every school—and to do it now, to make sure that blanket of safety is in place when our children return to school in January.”

While many Americans may agree with this sentiment, it is not an inexpensive proposition. According to the National Center for Education Statistics there are 98,817 public elementary and secondary schools in the country and 33,366 private schools. Moreover, the median annual salary for a police officer is $56,035 according to the Bureau of Labor Statistics.

So the bare minimum cost of putting a police officer in every public school is about $5.54 billion — closer to $6.4 billion if we add 20 percent extra to cover the cost of payroll taxes and benefits. And this doesn’t even include the cost of hiring and training these officers.

With the federal government currently running $1 trillion deficits and most state and local government budgets stretched to capacity, it’s worth considering other ways of fundIng such an initiative.

As a thought experiment, one option would be to levy a “Peguvian” tax on guns in the same way we put excise taxes on tobacco or polution as a means of offsetting the externalities that they impose on society. The challenge of these types of taxes is setting the tax rate at a level roughly equal to the cost it places on society.

So how much of a tax would be required to finance the cost of putting an armed police officer in every school?

Well, according to the the National Shooting Sports Foundation some 10.8 million firearms were purchased in 2011. So if we divide the $6.64 billion cost of 98,817 police officers by 10.8 million (we’ll ignore the private schools for the sake of this example), we get an excise tax of $615 for every new firearm purchased in America.

This is clearly a hefty tax to put on each firearm sold every year. But if the goal is to internalize the cost of protecting schools to the source of the danger, this is roughly what it would cost to do so. The other option is to shift the cost to all taxpayers, even those who may never own a gun.

Scott A. Hodge is president of the Tax Foundation in Washington, D.C., and is recognized as one of Washington’s innovative thinkers on tax policy, the federal budget and government spending.