I can't find anything, either, with regard to what the Patriots offered him. But knowing the Pats' history, I'm sure they lowballed him with the "promise" to go deep into the playoffs.
I'm sure money had something to do with it, but maybe culture is important to him, too. At the time he signed with the Bills, Allen was a question, but with a lot of upside. And it was a fact that Brady and Gronk were getting old.
Glad he chose us, either way.