Cal. Educ. Code § 39802

In order to procure the service at the lowest possible figure consistent with proper and satisfactory service, the governing board shall, whenever an expenditure of more than ten thousand dollars ($10,000) is involved, secure bids pursuant to Sections 20111 and 20112 of the Public Contract Code whenever it is contemplated that a contract may be made with a person or corporation other than a common carrier or a municipally owned transit system or a parent or guardian of the pupils to be transported. The governing board may let the contract for the service to other than the lowest bidder.