Get yourself a UHF handheld
	
	
		Get yourself a brand name handheld UHF transceiver.  The route you describe will be in use by heavy transport vehicles and they all carry a UHF.  Other 4 wheelers will carry a UHF.  I have had Unidens and I also have an ICOM.  They are both good however I feel the ICOM is a more solid build quality.  They are used by many organisations on other licensed frequencies, same units just different programming.
Along the Nullabor your likely to get mobile coverage, easy enough to check on coverage maps of the various network providers.   Judging by this info
Telstra - Our Coverage 
In an emergency on your route you’ll be fine on you mobile.