As PP mentioned, you have to pay a $200 deposit at time of booking and the balance will be due 30 days prior to your arrival. Between your booking date and payment due date, you can choose to make your own monthly payments if you want to, but Disney doesn't offer a formal monthly installment plan to pay it off. You should be able to make your payments right on
MDE.
Be aware that if you need to cancel, it can take some time to receive your refund. Sometimes its recommended to put your money in a savings account each month and then use the lump sum to pay off your trip closer to your payment due date. This way you have full access to your cash, rather than letting Disney hold it.