Cheap Cancun Vacations?

My original vaction to New Mexico to go skiing got cancled on account of there being no snow. My new destination is Cancun, Mexico. I have a family of 4 with 2 teenagers. We are looking for an all-inclusive resort on the beach. Including airfare, we are looking at the price range of 3-4 thousand dollars. No more than that. I know that is had to find, but if anybody knows of any good deals gong on for DECENT resorts, please let me know. I have looked all over expedia and had no luck. I am wanting 2 rooms for December 20th to 27th departing form dfw airport. Thank you for your help!