My friend left his wallet in a cab yesterday while he was in town. He got a call today from the cabbie who found it but since he's already gone the cabbie is going to drop it off with me and I will mail it to my friend. The wallet had $250 cash in it.

How much should I tip the cab driver if the money is still there and how much should I tip if its not? I already am paying the meter fare of about $70, if that makes a difference.