California Code, Family Code - FAM § 7553

(a) The compensation of each expert witness appointed by the court shall be fixed at a reasonable amount.  It shall be paid as the court shall order.  Except as provided in subdivision (b), the court may order that it be paid by the parties in the proportions and at the times the court prescribes, or that the proportion of any party be paid by the county, and that, after payment by the parties or the county or both, all or part or none of it be taxed as costs in the action or proceeding.

(b) If the expert witness is appointed for the court's needs, the compensation shall be paid by the court.