Some team is going to have to decide if they want Baby to start for them. If a team decides it wants Baby as a starter, then Maxwell's 8 million figure may be close (I would guess 7 tops but I don't know alot about it).
Max is wrong imo that the Celtics will sign Baby for 8-10 million to be a backup. The only way they would do that is if they had reason to believe that Garnett might have continuing knee trouble...but even then they could spend that kind of money on someone else or a combo of players...