I remember Imperfecto Ruin Pub at Ansal Plaza used to do buffet lunches for 399 onwards. You might want to call and check if they still do it.
Jungle Jamboore does a 7-course buffet starting at Rs 499! You cannot miss this one out.
It will cost you slightly above 500. It is available at Govinda's restaurant in East of Kailash for Rs. 530 on weekdays in between 12:30 to 3:30. Hope this helps 😊