I actually posted the same question a few weeks ago. the most common answers i heard:
Liberty Tree Tavern (I know its in MK, not what you want) but scores of people swear its the best place for thanksgiving
Thanksgiving at Fort Wilderness (same as Mickys backyard bbq). Seems nice but over $50 per adult
Trail End at Fort Wilderness. It's the cheapest buffet on property at $30 per adult, and it seems like a nice rustic atmosphere for thankgiving
All the usual buffet options that will run $40+ per adult... Chef Mickey's, Hollywood and Vine, Boma (african cuisine and traditional turkey and stuffing).
I think I'm going to try trail's end this year. I tried Hollywood and vine 2 years ago and it was awful, and $260+ for 4 adults and 2 children.