§ 203. Expenses incurred in the performance of official duty. 1. The actual and necessary expenses of all officers and employees, other than supervisors, paid from county funds incurred in the performance of their official duties, and the actual and necessary expenses of all supervisors incurred in the performance of powers and duties of the county, shall be a county charge. 2. The board of supervisors may authorize the payment of a reasonable mileage allowance for:

(a) the miles actually and necessarily traveled on official business by any such officer or employee, other than a supervisor, by the use of his own automobile; and

(b) the miles actually and necessarily traveled on official business of the county by any supervisor by the use of his own automobile, including travel on official business of the county in going from and returning to his residence. 3. Whenever the board of supervisors is directed or empowered by law to appoint a commission or board, by whatever title known, to render a service for the county, such board of supervisors may provide for the audit and payment of actual and necessary expenses incurred in the performance of duties including the mileage allowance. 4. No supervisor, officer or employee shall be allowed or paid any lump sum in lieu of actual and necessary disbursements incurred by him.