If you read my proposal for legislation above, you'd see that the folks I would cover in that law would already have those skills. Believe it or not, there is a large pool of candidates already in place. Legislation could cover insurance troubles. Make it a WOT issue. There have already been AQ memos seized naming specific schools that could be struck by terrorists.
Cheaper solution? That's already in place. Armed teachers would be a backup that is a vital layer of defense. Like insurance. You pray you never need it...but one day....
The only part of your proposal I like is the idea of hiring former military as teachers, but not for the reason you stated.