Around P600 if I recall correctly. Huge selection. The ala cart breakfast options are good and half the price.
Around 1000Php. (or US$20).
Personally, it is worth pigging out for BUT I opted to have healthier portions thus buffet does not excite me more than once a place. There are equally great food around the hotel, even some just at the bottom of the hill where locals find the price to be more within reason.
Get an answer from The Manor at Camp John Hay staff and past guests.