(a) The Superintendent of Public Instruction shall not approve, as a basis for computation of financial allowances for reimbursement of replacement expenses incurred by a school district for replacement of a class 1 school bus, expenditures which exceed the lesser of the following amounts:
(1) The difference between the purchase price of the bus paid by the district, subject to the provisions of Section 15272, and the amount received by the district for the sale, insured loss, or credit for the trade-in, of the bus.
(2) The amount computed by multiplying the "average purchase price" of the bus, as defined by subsection (b) hereof, by the percentage shown in the following schedule for the total number of years of service rendered by the bus as a school bus in the service of the district, or, in the case of a used school bus, the total number of years of service rendered for the district and for a prior owner or owners:
Total years Percentage for computing
of service replacement expense
(b) The "average purchase price" of a bus purchased during any fiscal year means the quotient resulting from dividing the purchase price paid for, by the number of, all new Class 1 school buses having a like number of rows of seats which were purchased by an districts during that fiscal year. The value of items required by Section 15272 to be deducted shall be excluded from the purchase price. The Superintendent of Public Instruction shall furnish to school districts a list of such "average purchase prices."