Money isn't going to be the biggest issue
A better question is how much power would you give Manning in order to get him here ?
He will almost certainly want a big say in the offensive scheme we run so Sherman and Philbin may need to be flexible here and Sherman may have to concede some control
He may well also want a say in personnel. For example he may demand a strong push to spend $$ and high draft picks on the OL at the expense of other areas of the team
I would think the team that bends over backwards the most is the team that will win the Manning auction