From the AP:

Alex Rodriguez and the New York Yankees have agreed on a $30 million marketing package based on home run achievements that could raise the total value of his new contract to $305 million over 10 years.

From Murray Chass:

The nonguaranteed part of the contract will be the marketing agreement, which the commissioner’s office and the players union have approved. The Yankees and Rodriguez had to keep changing the nature of the agreement to gain approval because players cannot receive bonuses for achievements like home run totals. ...

The contract will not have the kinds of award bonuses that filled Rodriguez’s $252 million contract. In the seven years he played under the contract, Rodriguez earned $5.5 million in bonuses, including $3 million for his three Most Valuable Player awards in the last five years.

The $30 million will be broken into payments of $6 million dollars each when (or if) A-Rod ties Willie Mays at 660, Babe Ruth at 714, Hank Aaron at 755, Barry Bonds at 762 and when he passes Bonds.