While I agree with your premise, I personally think someone like an Urban Meyer would cost north of $11-$12 million/year. This is not a hotly desirable job from a recruiting and location standpoint, and those are pretty big deals if you want to win at a high level in today's CFB world. And, personally, I'm skeptical that the university would pay something like that just for the HC let alone what they'd owe the assistants.
It's all speculation, of course. I just think Nebraska's inherent talent/recruiting disadvantages may come with a high price tag that's a) bigger than we think and b) something we're unwilling to pay.