Honestly, if Bo were to go, I think there would be a blank check. Fans would want a proven commodity, and those don't come cheap, especially after all the bs Bo has put up with. I think the answer is "Whatever it took"
I think it would depend on the experience of the coach. They are not going to pay a 1st time HC 4mil. But if they were to get someone used to making a lot more, they would have to open the wallet more.
