While I don't follow baseball a lot nor do I particularly care for A-Rod I found this blog covering the economic costs of A-Rod to his team. Scott Boras states that his client is worth $30 million a year for the next ten years. His reasoning is that A-Rod brings more people to the stadium to watch the games, and that he increases the viewers on Yankee's YES network. Boras is stating that A-Rod increases the demand for the Yankee's, overall increasing total revenue.
The blog also calculates the economic cost of A-Rod's salary to the Yankee's revenue. Stating that his economic costs are 2.3% of the value of the team. Compared to Barry Bonds (and does not play everyday) who's economic cost to the Giant's is 3.4% of the teams value. In the end A-Rod's economic cost is lower than other high profile player on other teams, and for the Yankee's the new deal would be a bargain.