"If you've seen the rates for police details at overtime pay, you'd realize that calling up the National Guard is really a low cost alternative for a show of force at airports."

Doubtful, at best. In addition to their regular pay you have to pay a whole slew of secondary support personnel such as clerks, armorers and the like, all of whom also are called up (and paid) to issue the guns and ammo and account for each round as it is turned in etc. Plus commo, maintenance, etc etc...

That off duty police officer is coming at a flat X/per hour and requires none of the secondary personnel/equipment support. Plus frankly, the police officer probvably qualifies more often and is more proficient with his weapon AND has the power of arrest. Far more useful in an airport environment than guys standing around in black berets (Thank the "Army of One" Shinseki for that stupidity) chatting up the security women.

Regards,
-Bouncer-
PS: I've nothing against the black beret if you like dressing up as a frenchman.. doesn't do much to keep the rain/snow off your face or shade your eyes in summer though. Tactically it looks cool but isn't useful. Therefore it's dumb. Morale wise it pissed off terribly every ranger who ever earned the right to look french. AND WHY ARE THEY WEARING COVERS INDOOORS AT ALL!!!