The budget provided for in Section 67-4-9 N.M. Stat. Ann. shall provide for engineering, supervision, superintending, automobile travel expenses and other overhead expenses and for the compensation of county road superintendents in counties where the county road superintendent plan is adopted, for such overhead and other expenses of the state transportation commission in counties where the state transportation commission contract plan is adopted and for the compensation of road supervisors where the road supervisor plan is adopted. The total expenditures for all the foregoing purposes in any one fiscal year shall not exceed ten percent of the total county road and bridge budget up to and including fifty thousand dollars ($50,000) and five percent of the budget in excess of fifty thousand dollars ($50,000) and up to and including seventy-five thousand dollars ($75,000) and two and one-half percent of the budget in excess of seventy-five thousand dollars ($75,000).