It will vary on many factors such as location, years of experience and etc. To become a bat boy for a Major League Baseball team, you need to be at least 14 years old and in decent physical shape.
What we found is the salary for a New York Yankees Bat Boy from Glassdoor.com which is averaging around $13,646 (Base Salary of around $7,897 plus tips that would be around $5k to $6k). There are also some sources suggesting that the daily pay for a bat boy for the New York Yankees is $21.50 for six hours.
The batboys of the Giants on the other hand were getting about $55 a game - no matter how many hours they worked. - sfchronicle.com.
For ball boys, what we found is a 2007 issue of Clevelandmagazine.com stating that Cleveland Indians' bat boys and ball boys are paid $6.85 per hour.
In an article of New York Post published on August 7, 2011, former batboy for the New York Yankees Luis Castillo shared that Derek Jeter and some of the other guys were terrific tippers.
"Roger Clemens gave me $3,000 at the end of the year. Posada gave me $7,000. A-Rod might come in with $1,400. Sure, it’s still a sizable amount, but when he found out that other players were tipping higher, he had to imitate them, and he bumped his tips up. In fact, he had to make sure he was the best tipper in the league. He even tipped me $100 a week to make sure there was a creatine shake waiting for him after each home game."
Just recently, the foundation that runs a baseball tournament where a 9-year-old batboy suffered fatal injuries decided to pull all bat- and ball-boys and girls off the field for the remainder of their 2015 season. Find out more at nbcnews.com.