Via Buster Olney of ESPN:
Sources: Yankees had talked about signing Balfour in possible sign-and-trade before Soriano agreed to terms with NYY, Balfour with OAK.
The Yankees eventually gave up their draft pick for Rafael Soriano, but apparently they wouldn’t for Grant Balfour. They did like him enough to try a sign-and-trade, but those pretty complicated to pull off. Teams are essentially trading away their draft picks and permission is needed from the player involved.
It seems like the Yankees tried to work out a deal for Balfour, failed to figure out a way to get it done and then resigned to the fact that they would have to give up a draft pick for a reliever, they signed Soriano. If they had to give up a draft pick for a reliever at least they got the best one on the market.