Complex sentence: The principle of the airport construction was that the costs should not to be borne by the tax payers, so the entire airport would be built with borrowed money, through Oslo Lufthavn AS, a subsidiary of the Norwegian Airport Administration.
Split into simpler sentences: The principle of the airport construction was that the costs should not to be borne by the tax payers. As a result, the entire airport was built with borrowed money through Oslo Lufthavn AS, a subsidiary of the Norwegian Airport Administration.