California Code, Code of Civil Procedure - CCP § 1141.28

(a) All administrative costs of arbitration, including compensation of arbitrators, shall be paid for by the court in which the arbitration costs are incurred, except as otherwise provided in subdivision (b) and in Section 1141.21.

(b) The actual costs of compensation of arbitrators in any proceeding which would not otherwise be subject to the provisions of this chapter but in which arbitration is conducted pursuant to this chapter solely because of the stipulation of the parties, shall be paid for in equal shares by the parties. If the imposition of these costs would create such a substantial economic hardship for any party as not to be in the interest of justice, as determined by the arbitrator, that party's share of costs shall be paid for by the court in which the arbitration costs are incurred. The determination as to substantial economic hardship may be reviewed by the court.