The total cost of preparing plans, specifications and estimates, of the necessary property including damages to property not taken, of securing bids, and of the work, in grade separations, shall be borne by the railroad company or companies and the state: Provided, however, That unless otherwise agreed upon, said railroad company or companies involved shall be liable for ten per cent of such total cost: Provided, further, That all right-of-way, owned by the state or the railroad company or companies and needed and used for such grade separations, shall be donated for that purpose and shall not be considered as a part of such total cost to be prorated between the parties involved.