The cost of baseballs to MLB is about the same as a starting first baseman. MLB runs through about 900,000 balls in a season, for $5.5 million. The average first baseman is making $5.7m in 2005, based on the top 30 salaries for the position at USAToday.
Of all the sports, baseball seems unique in treating its spheroid as almost instantly depreciated by contact, and disposable. Mike Maloney and I were discussing this issue on the way back from a fishing trip this week. Then on my return I find that Frank Stephenson had unearthed a column titled "The true life story of baseballs." By this story's accounting, the practice of players tossing balls into the stands - the observation motivating the conversation with Mike - accounts for less than 10% of balls retired from an MLB game. A foul ball into the stands is the modal cause of retirement, with foul tips (they must scuff the ball somehow) second.
Unlike a basketball or football, a foul baseball seems more easily captured and hidden by fans. The differential cost of policing the team's "right to the ball" may be a factor causing baseball to "let them go," while basketball and soccer manage to get their balls returned.
Two questions spring to mind when thinking about crowds and the cost of balls. First, does any baseball historian know when MLB quit trying to get balls back from the crowd? My hunch is that the "rule of capture" in baseball was established in the post-war period, and was not common practice during the depression.
Second, colleges rely on the goodwill of fans to return footballs to the field. Why then does the NFL resort to nets behind the goalpost to force the ball's return? Whatever the reason, viewed alongside practice in baseball, the NFL's nets seem miserly. Footballs are more costly than baseballs, but not as many leave the field. At $200 per ball and 10 balls per game, the NFL's cost per game of souvenir footballs would be roughly the same that baseball incurs at present. Relative to the cash collected from fans in the seats, it's even less.