Ashley:
The least expensive way for your family to stay at Walt Disney World is to consider the
Value Resorts. Because you will be coming from Georgia and most likely bringing your own car, upgrading to a Preferred Room near the buses does not have to be a priority either. For families on a budget, I recommend the Magic Your Way Ticket that gives you one park per day. Not purchasing the Park Hopper option will save a family of 9 significantly.
The word 'best' means a lot of things to folks, but I'm going to guess that 'best' in your book is aimed at the least expensive time of year. Lucky for you, the Law of Supply and Demand also means that the least-expensive time of the year also sees low crowds, another benefit for guests. Look at Disney's Value Season months to book your trip and get the best rates: January through mid-February, September, and mid-November through mid-December except for Thanksgiving Week. Additionally, Florida's weather is mild during Value Months, except on the front-end of September. If I had to narrow the choices, I'd look at November because of its Christmas decorations.
Unless your children are between the ages of 3 and 9, I don't recommend the Dining Plan. Our family has found that paying the adult price for a junior high child is not worth it and the amount of food we must eat to justify it doesn't work for our family. However, we have found that the price of the Basic Dining Plan that includes one table service meal
is a good value if all of your children are in the 3- to 9-year-old range because the cost of a Character Meal can almost pay for the child's daily rate on the plan and those are typically the meals you will seek for that age.
Wishing y'all a magical vacation!
Whitney