If any real property which was acquired or used for fair purposes and which was purchased or improved in whole or in part from funds apportioned or allocated to the county for fair purposes by the state is sold by any county, there shall be paid into the Fair and Exposition Fund in the State Treasury from the proceeds of the sale an amount equal to that proportion of the cost of the real property and improvements which was paid for out of funds apportioned or allocated by the state for fair purposes, less a reasonable allowance for depreciation in value in an amount approved by the Department of Agriculture.