Whenever a school district has contracted for the purchase or lease of a factory-built school building and where such building is to be supported by foundations, underpinning, pedestals, or similar type elements which extend more than 18 inches above natural grade at any point, or on temporary blocks or jacks of any height, all the provisions of Article 3 (commencing with Section 17280) of this chapter shall apply to the design and construction of onsite work except that, for fee purposes, only the estimated cost of onsite work need be considered. The minimum amount in any case shall be fifty dollars ($50).