What is the missing number?

A letter written in a childish scrawl came to the post office addressed to "God". A postal employee, not knowing exactly what to do with the letter, opened it and read: "Dear God, my name is Jimmy. I am 6 years old. My father is dead and my Mom is having a hard time raising me and my sister. Would you please send us $500?" The postal employee was touched. He showed the letter to his fellow workers and all decided to kick in a few dollars each and send it to the family. They were able to raise $300.A couple of weeks later the same post office received a second letter addressed to God. The boy thanked God for the recent infusion of cash, but ended with this request: "Next time would you send the money directly to us? If you send it through the post office they deduct $200."