The problem with living underground in the wetter areas of the world is that holes have a nasty habit of filling with water at the very worst, and at the least you will have nasty problems with damp, mold and mildew. These problems can be overcome if you prepared to put the time and effort into it but its not as easy as most seem to think, unless you live in a dry area with stable well drained subsoil and a low water table.
Every thing is a compromise no area will tick all the boxes. You can buy 1/2 and acre from ***** for $50,000 dollar that has a good reliable rain fall and I imagine reasonably fertile soil and I'm also guessing has no infostructure on it or you could have bought a working opal mine(make a good bunker) with a tidy little cottage that was partly furnished along with some gear to work the mine for $20,000.
At the barest minium I'm guessing that you would need at least $100,000 to drop a shed and a caravan on sambos block to make it habitable. Most people would end up spending closer to $400, 000 on a block like that. Compare that to lightning ridge example I gave above of $20,000 and virtually nothing else to spend. If your lucky and know what your doing you might evan be able to make the mine pay for itself.
That extra $80,000 to $300,000 you saved moveing to lightning ridge as opposed to next door to ***** can buy you a lot of preps.
Its a bit like selling a old bom second hand car and having the guy say he doesn't like the dint on the door, the faded paint work and sticky clutch. But I'm only asking $500, if it was in prestine condition I would be asking $5,000 for it. People want every thing and to pay nothing for it.
Another example is a know a bloke that bought a house in Fords Bridge a little town literally the back of Burke for $5000 so he had some were to go and stay and go shooting. The house was a real dump but liverable with about 10 ac just across the road from the pub(the only thing of note in the town). You wouldn't grow much out there but there is plenty of sheep and cattle and game both feral and native along with fish and yabbys in the Wargo river near by.
Despit what people will tell you in out back areas there is often quiet a shortage of labor so often work isn't as hard to find as you would expect.
The outback isn't for every one, but survivalist in particular don't give it due consideration it deserves. As I said above, google James M Dakin's blog he describes what I'm referring to fare more eloquently and with much more wit than I can