Any area not within an organized township or city must be assessed by a certified assessor under the supervision and direction of the county director of tax equalization. The county director of tax equalization may serve as an assessor of property under this section. Every individual performing assessor services under this section is entitled to compensation and mileage and travel expenses determined by the board of county commissioners for the time actually and necessarily employed in assessment of property. The compensation and expenses must be paid from the treasury of the county in which the assessed property is located only upon submission of an itemized statement setting forth the actual time spent in the work of the assessor and mileage traveled, approved by the board of county commissioners.