The most cost effective and ultimately the only long term solution for the region would be to invest heavily in the region's rail and road links. If travel times to BFS were reduced, then there would be a lot less need for LDY in the first place.
The main issue is that the money that could fund such investment projects is currently being spent on keeping LDY open. The question is do we close LDY and then invest in the road/rail network using the money made available, or do we wait until alternative funding is found for infrastructure, and only close the airport once the new roads are open?
The first option would be the most efficient and the quickest to implement, but would the local community accept short-term pain for long-term gain?