I am a bargin hunter/couponer/ always do my research to find the best deal BUT when we do Disney, I ALWAYS book through them. If you book a package, it is the $200 deposit as pp said. You can pay as little or as often as you would like after that. There is a full refund if you cancel 45 days before your arrival date. Booking with Disney is easy becuase it is one stop shopping. One number for questions, concerns, changes, ect. As I am sure you have read on here, if you go through disney, always ask if there is a pin code attached to your name for a discount. If not, call back in a few days and ask again. Keep your ears open for discounts throughtout the year. They only allot a certian amount of rooms for that discount, so if you are already booked, you just call and have them apply it to your total. We even book air thought Disney. We fly air tran, and the last two times we went the EXACT same flight was cheaper through Disney than AirTran/Expedia/orbitz ect. Be aware though that if booking air through Disney at the same time as your package, you must pay the flight porition in full when you book it.
Bottom line is that if there is ever a question or descrepency (sp?) in your reservation, you have one company to call, and they can help you easily while you are there. I like the ease of it. Plus- No other company tells me to have a "magical day" when we hang up.
Oh, and if you do a room only ressie the deposit is equil to one night stay... and depending on where you stay could be close to or more than the $200 deposit for a package. A cm recently told me that if you change to a package later they actually cancel your ressies and start over, to book the package. Not a big deal at all, but for the price of the deposits it might be easier (and even less $ up front) to just book the package to start with and not have to worry about it KWIM?