The taxpayer, as usual, will pay for it. Again, I consider protecting children from madmen to be a worthy cost.
We have armed security on the streets every day. We call them "police". Innocent bystanders being shot by police are few and far between. Maybe armed security isn't the be all to end all. Neither is "GUNS BAD!!!!" Banning this, banning that does not prevent my two shotguns, bag of shells and a classroom of 6 year olds scenario from happening. Unless, of course, we're going to ban the standard hunting shotgun.
And, for the record, I posted the NRA's idea before they formed it. I'm awesome.