Cal. Educ. Code § 17089.2

Any portable classroom that is leased from the board by a school district or county superintendent of schools under this chapter on or prior to December 1, 1991, may be purchased by that district or county superintendent of schools for an amount equal to the purchase price paid by the board, including the purchase costs specified in subdivision (c) of Section 17088.7, less the amount of any rent already paid to the board by the district or county superintendent of schools for that classroom. Payment for purchases made pursuant to this section shall be in equal annual installments for an agreed upon term not to exceed nine years.