I just finished a 12"x18" one layer sheet cake(carrot with cream cheese icing) Made fondant farm animals and barn. airbrushed sky blue and grass green) Charged $150.00 for it and she was more that happy with the price. Sheet cakes can be a lot of work. I don,t set a price. I figure everything before I give the price. If they want it, fine , if not fine. I usually get to do it. If they got the money , honey, I got the time. lol!!!