Ways to save money on DCL cruise:
Either book early, or very late. The prices tend to go up as time goes by. But when booking opens, the first couple days of booking are open to gold and platinum members only - a perk of frequent cruising. So sometimes the prices go up even before open to general public. They will often stay at that rate for a while, but Disney ups their prices every few months. However, after the paid in full (PIF) date - the date that anyone going on the cruise must pay or lose their deposit, usually a couple months before sailing date - DCL may offer "guaranteed" rates. These are discounted, non-refundable fares where you choose the type of room you want (inside, verandah, etc.) but not the location. The location is chosen by DCL a week or two before the cruise. Often times these "last minute" deals are about the same or not much more than the prices shortly after booking opened. However, these rates are not always available, especially on very popular sailings
For DCL, anytime traditional school is not in session - summer, spring break, Christmas - are popular and expensive times to cruise. If you can cruise off season you will pay significantly less.
Generally speaking, the shorter the cruise, the more you pay per person per night.
Most travel agents get a commission, and they will pass that savings on to you in some form. For some, this is pre-paid gratuities, or free dinner at Palo. If you book through Costco you get cash back - I think it is up to 8%.
If you have a DCL Visa, you can use reward dollars to pay for the cruise. You also get 6 mos. to pay for the cruise (for purchases made directly with DCL), and up to 2% cash back on the purchase.
If you have a way to obtain Disney Gift cards at a discount (from Sam's Club or BJs) you can use them to pay for your Disney cruise and save. The usual discount for these stores is 3-5%, but sometimes can be as much as 8%. Make sure you don't get the ones that are only good at the stores, but are good at any Disney location -cruises, hotels, etc.
Once you do cruise, you can book a "placeholder" cruise on board. This is a future cruise booking - you don't have to know exactly when you will cruise - that gives you 10% off and an on-board credit (cash to spend on board) of $100-200, depending on cruise length. You have to put down 10% of the cruise cost as a deposit. You have 2 years to use the placeholder. You can hold onto it, then switch it to a cruise as soon as booking opens, but you must sail within 2 years of the date you purchased it. Also, if you designate a
travel agent when you book (such as Costco) you can still get their cashback and the 10% off.
The best of all worlds is to do an onboard booking (10% off + $100 at least), using Costco (maybe another 8% back), and paying with discounted gift cards (5% more) using a Disney Visa to buy the gift cards (2% back at big box stores, but of course you don't get 6 mos. to pay that off). Costco does allow you to use Disney Gift Cards to pay for your cruise (not sure if all travel agents allow that). Of course, you can't do all of this until you have cruised once, so you can't use the 10% off on the 1st cruise.