My only information on the specific topic is this thread here, but I would like to point out a couple of things.
First about the cost. It is quite possible that the Boeing offering beats the EADS one on a plane to plane life cycle cost comparison. But that does not mean it beats it in on a fleet level comparison. It is possible that due to the EADS plane being larger and having longer range that less planes are required to fulfill the same role.
The extended range is also a mitigating factor as far as the smaller selection of airfields goes. In the current global environment that the new tanker will be operating, the possibility that its home base will be threatened by enemy action is almost negligible, therefore the ability to use smaller airfields is no longer relevant to survivability but only in its ability to be at the needed space in the needed time, something that can be achieved from fewer airfields if one has longer operational range.