Celtics. At that time, $1 Million was more than the rest of the team was making combined. And by "team" I don't just mean the players. IIRC, I read that the coaches, the front office staff and players combined all made less than what Cosic was offered. All this talk about increasing coach salaries (and players in pro sports too) makes that $1 Million offer seem quaint. Even adjusted for inflation.
Side note: The fact that Cosic turned it down because he wanted to spread the gospel and basketball to his native part of the world is truly remarkable.