Scott Frost was making $2M/yr at UCF. So if he'd stayed there from 2018 to today, he would have made $6M in that time-span.

By going to Nebraska he made $5M each year in 2018, 2019, 2020, 2021, and then is fired after this year, they'd owe him a $15M buyout.

So earnings from 2018 through 2021 at UCF: $6M
And at Nebraska: $35M

Let's keep everything in 2020-ish dollars to not deal with inflation and assume that UCF would have given him a raise to $3.5M in 2023 when they go into the Big 12, and kept him at that effective rate (with inflation adjustments).

So then from 2018 to 2035 (when he turns 60) Scott Frost would have made $55.5M at UCF

Whereas he's made $35M already at Nebraska and would have another 13 years to earn the extra $20M, which seems quite likely, even if just as an OC or HC at a smaller school. So there's almost no downside and the possibility of huge upside if he does well there.