money for the bus driver

Hi friends,

The school bus drivers and cleaner will expect some money from us yearly once may be during the festival time. I missed at that time. I don't have any rough idea how much everybody will give. My son is in 2nd grade. Please tell how much I can give so that they will be happy. Don't think that silly question i am asking.means I don't want to give very less nor more money.

Thanks.