Hi, Teresina! We do not have any information regarding an extension of the fabulous buy 4 get 3 free deal that is currently being offered, but it is a phenomenal discount, and I'll keep my fingers crossed that you find something just as good!
As for best possible price, it's going to depend on when you are going, what you are looking for, and who you book with. I personally know the people at
www.themagicforless.com and have booked a few trips through them. The thing I like best about working with them is that if a discount offer comes up that you qualify for, your agent with them will automatically work to get you the discount without you having to contact them and ask. I think that's terrific service!
You can also find some discounts offered through AAA, and if it doesn't matter whether or not you stay on Walt Disney World property, you can check any of the travel websites like Expedia, Travelocity, or Priceline to see what hotel discounts might be available.
I don't know when your birthday is, but the best value at Walt Disney World is going to be during low season. You will find less expensive rooms then, which makes the Magic even more affordable.
Happy birthday in advance! I hope you find the day sprinkled with pixie dust!