How much does Mr. Bumble demand for information about Oliver?

It's not the henpecked Mr. Bumble who negotiates with the sinister Monks, but rather it is his wife. They settle on a figure of twenty-five pounds (quite a tidy sum; roughly $2,000 in today's money). Neither of the Bumbles know it, of course, but Monks is in fact Oliver Twist's half-brother and has crawled out of the woodwork to make sure Oliver doesn't get the inheritance to which he's rightfully entitled.
Monks pumps Mrs. Bumble for information as he wants to make sure that all traces of evidence that might link him to Oliver or his mother are destroyed. That explains why he's so interested in the gold locket stolen from Oliver's mother, Agnes, by an old crone and then subsequently redeemed at the pawn shop by Mrs. Bumble. The locket is a keepsake of Agnes's and contains a wedding ring with her name carved on it and two locks of hair. Monks is determined to ensure that Oliver will never discover his mother's true identity nor claim his inheritance, so he ties down the gold locket and throws it into the river.