The cost of establishment of a county sewer district and the furnishing of the improvement therein shall include the amount of all contracts, the cost of all lands and interests therein necessarily acquired, the cost of erection of necessary facilities and appurtenances for operation or administration of the improvement, the cost of necessary equipment for operation or administration of the improvement, printing, publishing, interest on loans, legal, engineering and other professional services, and all other expenses incurred or occasioned by reason of the establishment or extension of the district and the furnishing of the improvement. In addition, there shall be apportioned against, charged to and included in such cost, such allowance as the county government may make for expenditures which are directly attributable to the establishment or extension of the district as well as for any services rendered by the attorney for the county government, the County Engineer or any other salaried county officer or employee when such services have been necessary to or occasioned by reason of the establishment of the district.