You can get a good deal if you ride-share, in this case. If you have too much luggage, the flight won't be viable either, so it seems like a doable comparison.

If I am reading the map correctly, mountains would come in the way, for a straight line path, but that is not a good enough excuse for not having high speed rail from Yelarbon to Burra, when there is a rail along the coastlines.

And since I don't know better, I am going to assume that train cost is dues to coastal maintenance costs.