AZ and Daas Yochid, I think your right. People who get paid for their work, are certainly more motivated.
One issue I do take with you, AZ, is the exact amount. In other threads you felt that a date 2 should automatically get a certain amount. Sometimes people agree to a second date after a dismal first date, due to the excuses being offered.. If a person knows the second date will definitely cost them, they may hesitate and refuse to even try. I think if the second date turns out like the first, an acknowledgment of $20/30 dollars should suffice.
Otherwise, I do feel your number for a second date makes sense.