yep 2-3% of their bodyweigt or expected body weight. Younger puppies would eat more upto 10% of their bodyweight ( Im talking weeks old puppies ) but it does depend on energy and exercise.
Mum's eat one carcass a day (if it's big they don't get through the whole lot) and we buy 4 chicken carcasses at 0.70p but I think most RAW places online are about 0.34p for 454g (1lb) which would be about two small chicken carcasses.