Uh, at Sandy Hook that would be $280,000/yr. I think they can find a part-time armed guard for less than that.
You get what you pay for. If you can get a well armed guard that can handle someone with a Bushmaster with taped together 30 round magazines, then get them. That person will still need to live near the community to work in the school Perhaps a retired police officer in the area? Should each local district make that decision and come up with the funds? What about poor districts?
Here is a solution that costs way, way less than that. Some training, a weapon, done.