Hi Jacqueline,
Often times, the amount of the deposit is based on when you book your vacation. For example, if you are booking less than 45 days out, you will need to provide a night's deposit or a percentage of the trip. If you are booking longer out, you might need less money to hold your vacation.
In addition, even though Disney is booking your vacation, the airline they are booking with could have different requirements for payment. This could mean you need to pay part or all of your airline fees up front.
Finally, there may be a special promotion which requires only $200 deposit. It may not be offered at all times of the year or for all vacation packages.
I always recommend calling Disney at 407-WDISNEY and asking the cast member if they know of any offers not published on line.
Wishing you a magical vacation!
Beth