The final contract cost shall be determined after inclusion of the net change due to additive and/or deductive change orders. If the final contract cost results in an increase above the original bid amount, the school district shall finance the entire increase. If the final contract cost results in a decrease from the original bid amount, the school district and the state shall share the amount of the decrease based on the state funding assistance percentage in effect at the time of contract award. Copies of all change orders when executed and signed by the school district's authorized agent and the project architect/engineer shall be forwarded to the superintendent of public instruction.