60 people can be served easily in 15-20 minutes using a buffet line----this is good because the guests are all eating at the same time. To serve 60 people with servers and plating the food in the same amount of time would require 6 servers and 3 staffers plating the food. If servers are used the certainly China will be used rather than paper plates. Rental plates run 85 cents here and set of silverware runs 75 cents----that's $1.60 rental cost per guest. The plates will have to be picked up and returned clean to the rental agency----picking up and returning involve time and fuel. Washing the rental pieces requires labor. With paper plates, guests usually "bus" their own tables---depositing paltes and plasticware in trash cans. China and silverware will require that the caterer busses the tables----more labor.
Guests all like different things----some rare---some well done----some sauce----some no sauce, etc. Put yourself in the customer's shoes----sell them the fact that it is better for their guests to plate their own food ----it is better that guests are served quick and eat together.------The customer does not realize the costs of servers, or they wouldn't even ask-----if you do not "sell" this concept, and simply bump the price----they will balk at using your services. Paying 9 extra people $10.00 per hour for a minimum of 3 hours will cost $270.00 in just labor. Do not just raise the price without explaining the problems