The term "estimated cost," as used in this section, means the reasonable value of all services, labor and materials and use of scaffolding and other appliances or devices entering into and necessary to the prosecution and completion of the work to ready a building or structure for occupancy, provided that the cost of excavation or grading, and of painting, decorating or other work that is merely for embellishment or not necessary for the safe and lawful use of the building or structure, is not deemed a part of such estimated cost.