Welcome aboard, Patina! I'm glad you're considering booking a cruise on one of Disney's amazing ships!
Disney Cruise Line's
payment information is pretty clear about the final payment for most staterooms being 75 days prior to departure. However, there are a few things to keep in mind. This payment is just for the cruise itself. This doesn't include any Port Adventures, Adult Exclusive Dining reservations or extras like that. If you are able to pay the cruise off by 75 days out, you'll be all set. Any extras will be put on your stateroom account which is not charged until the end of your cruise.
A way we like to save money for our cruises with Disney is to purchase a few Disney gift cards throughout the year leading up to our sailing. We purchase them at our grocery store which offers double or triple fuel rewards on gift card purchases, so we save some money on gas which we need anyway. Then we use the gift cards to apply to our cruise payments. You might look into doing that to help cut the costs a bit and still be able to pay off your cruise by the 75 day mark.
I hope this information helps, Patina. Disney cruises are truly gifts you give your family that build lasting memories you'll never forget. Happy planning, and let me know if I can help with any other questions!