Opportunity cost is not some esoteric concept. It's not controversial, nor is it in of itself at the center of this debate. The problem here is your inability to coherently apply the concept to baseball or to comprehend the meaning of my argument. There is no question that spending 13 million dollars on Greinke means the Brewers have less money available than they would otherwise. They could have spent that money on another player, as you suggest, used it for player development, or used it to renovate their offices. However, none of those things impact the value of Greinke's contribution to the team. The talent level of a given team exists independent of the team's payroll. A given 25 players have the exact same talent regardless of whether they are paid 100 million or 60 million dollars. It is true that more payroll flexibility gives the team the ability to hire better players, but that isn't what we are talking about. We are estimating the change in talent level of the Brewers, represented by expected wins next season, from the Greinke trade. The only things that matter in this equation are the abilities of the players in question -- i.e., Greinke, the pitcher he is displacing, the shortstops they swapped, and the other traded players. Of course payroll is important to the Brewers, and of course there are limits to what they can spend. However, that does not make it logical to discount Greinke's on-field value to the team by his payroll, a factor which does not impact his performance for the team. If you're trying to make the argument that Greinke's payroll is a significant downside to the trade, then you are doing it the wrong way. If you are trying to understand how opportunity cost works within the framework of baseball, then you are not quite there.