They don't play the same position. They're not going to stick Milano into Edmunds' role to have him cover large zones and the intermediate middle. Milano and Edmunds have different roles and they work great together. Another poster brought this up, as if the Bills could just swap them. It doesn't work like that.
So, if you want to replace Edmunds, that's fine. He seems to be the odd man out, money-wise. Not role-wise. But to find a player with the same intangibles and abilities, you're going to be looking in the mid-first round again, unless he has some serious question marks/injury. Or if you're looking in FA, then you have to overpay.
I think it's most likely that the Bills pay the man they drafted and developed, instead of using valuable resources on someone brand new.