Supposedly somewhere between $5-7.5 million but it wasn't just about the money. He wanted to be a HC. And it's not like he's going to quit or get fired after one season when they are playing for the #1 pick. But if he does, he'll be cheap (because the Saints will still be paying him).
It also wouldn't be about the money on the Eagles side. You just don't pay coordinators that kind of dough. It would have a ripple effect on the HC, the DC and maybe even some players.
The more interesting question, as ever, is does the OC really make that big a difference in terms of scheme and play calls or is the real difference having an OC who isn't an extension of Nick?