With such a short trip I would not want to spend it listening to a timeshare pitch. That two hour presentation can quickly eat up four hours of your day, from what I've read/heard.
Must you absolutely go this month? It will be beautiful, but SO crowded. If you could go in January you would accomplish a lot more in your limited amount of time.
Otherwise, I would go with Priceline or Hotwire and see how low a price you can get on your hotel, like the MouseSavers family did. That could be a HUGE money saver!
I would also plan on off-site meals whenever possible. Otherwise, Disney's counter service food isn't too terribly high-priced, IMO.
Hmmm...
Gas 100.00
Tickets 587.00 (3 one-park, one-day tickets...164.28 adult, 129.13 child)
Hotel 120.00 (40.00/night x 3 nights)
Parking 24.00 (8.00/day x 3 days)
Meals 220.00 (55/day...breakfast in your room from things you can take with you--doughnuts, granola bars, pb&j, etc--one counter service meal onsite 30/day, one meal offsite--McDonald's or other inexpensive place 25/day)
That totals 1051.00...did I forget anything?
That would give you three park days, and one day for Downtown Disney, or Fort Wilderness or something...maybe touring resorts to see decorations, AKL to see the animals, etc. Keep in mind that anything additional, like mini golf, will be an added expense. Disney Quest would be great for kids the ages of yours, I think, but would cost 80.00 additional with tickets through TicketMania. As far as parks, I would do two days at Magic Kingdom, and the other day at MGM Studios, JMO, of course. I like AK, but they close earlier with no fireworks. Epcot is great also, but with limited time I would skip it. I think your kids would prefer SpectroMagic, Wishes, and Fantasmic to Illuminations. Again, JMO.