Pizza Planet, The Cheyenne/Santa Fe, Restaurant des Stars are under €25 for adult buffet. The rest are around €30 and upwards.
We budget €100 euros a day, for everything, 3 adults, 1 child. We work out where we are gping to eat before hand and make sure we eat twice if counter service or one buffet plus breakfast. All of us sometimes have kids meals so that the money we save, goes towards the last day.
One trip however, we took €450, for 5 days, and added and extra night off site for €35 because we ate off site for €25 (2 adults, 1 child) and didn't want to leave!