I don't have anything constructive to tell you about your glass prices, which is a crappy situation, and I feel for you....
But back to the tempering-
Tempered glass is usually expensive as hell. I honestly don't think it is needed for a regular cab. If you are concerned about safety, you could always get some clear, or lightly tinted window tint on it. That way, if someone goes nuts and breaks it, it's not going to shatter into big dangerous chunks. The tint will keep it together, and hopefully nobody will get cut.
Tempered glass is good for taking blunt force, but force in a relatively wide area, could cause it to explode. Is that "widearea" as big as a fist? That I do not know. One thing I do know, is I'd much rather clean up normal glass than tempered glass!
(I used to be huge into fish tanks, and have drilled tons of holes, and have run into my fair share of tempered glass problems)