NRA Solution: Armed Guards at Schools

The NRA’s solution to prevent tragedies like those at Sandy Hook Elementary and Columbine is to have armed guards in every school. Leaving aside the fact that there was an armed guard at Columbine, and assuming that armed guards is a viable solution, consider the costs of such a policy.
The area where I live has relatively small school districts. Even so, the costs of an adequate number of guards would probably be in excess of one and a half million dollars a year. Multiply that by the number of schools throughout the country, add in the colleges and universities, and the annual costs would run into many billions.
Both safety and freedom have their costs. Since guns are the reason for the guards, the costs should be met through taxes on guns and ammunition. They would probably end up being substantial, but, hey, that would be the cost of “freedom” of ownership.