Wow, that will be REALLY tight! Is there any way you could make/save more money before your trip?
Here are some tips for saving money -- sit-down restaurants at WDW are less expensive for breakfast and lunch. Dinner at the counter service (fast food) restaurants is the same price as lunch, so if you plan to have one meal at counter service and one at a sit-down restaurant, go to the sit-down for lunch and the counter service for dinner.
Instead of ordering alcohol or soda ($2 each) with your meal, order ice water which is free. If you are yearning a soda, order a large and share.
Food portions at WDW are quite large -- consider sharing one meal between the two of you. (DH and I will often split a meal and then share a snack a few hours later.)
Adults can't order children's meals at sit-down restaurants, but can order the children's menus at counter service restaurants. On a recent trip, for $3.99, I was able to get a small soda, chilled grilled chicken, vegetables and dip, and crackers -- very filling.
If you really want to dine at a sit-down restaurant and would prefer to dine closer to dinner time, make a reservation for the latest lunch slot available (often around 3-3:30 p.m.). You'll dine closer to dinner, but be charged lunch prices.
Consider eating two meals and a snack -- say breakfast, late lunch and a snack in the evening.
Instead of purchasing bottled water, drink from drinking fountains or ask for a cup of ice water at one of the counter service restaurants.
Avoid shopping in the parks. We always go to the World of
Disney store in Downtown Disney to pick out one souvenir each towards the end of the trip.
I hope this helps!