It is difficult to give you a concrete number since the cost will be in terms of food style and quality, such as Shanghai dish, western food or indian food. The price may also vary greatly from CNY20 to over CNY500. I think you could refer to these restaurants' average cost listed here. And, no tip is required in China, unless you eat or stay at these 5-star rated hotels. Usually, service charge of 10~15% is required for a buffet and CNY5~10 tip is ok for hotel staffs.