Buying a car from interstate

From this link http://www.rms.nsw.gov.au...tion/unregistered.html
 NSW permit looks easier and less messy than SA permit. Also valid for 28 days whereas SA appears to bhe only 3 days.

Unregistered Vehicle Permit (UVP)

An Unregistered Vehicle Permit (UVP) allows you to drive or ride an unregistered vehicle on the road network for a specific journey.
Permits are valid for up to 28 days, and allow for a:

• Single journey from A to B
• Return journey from A to B to A
• Number of defined trips to be completed within 28 days, for example from A to B to C to D
• Specific purpose over a number of days, up to a maximum of 28. For example, for harvesting during a defined period.Unregistered Vehicle Permits provide limited access to the road network. They are not intended to cover the regular use of a vehicle on a road or road-related area.
  

  Interstate recognition

  Permits issued in NSW are valid in all states and territories. NSW recognises permits issued in all other jurisdictions provided the vehicle is operated in accordance with the conditions of the home jurisdiction.
  
  A permit may be issued for a vehicle starting its journey in another jurisdiction and travelling to NSW. A permit must not be issued where the journey is entirely within another jurisdiction.
  An Unregistered Vehicle Permit must not be used as a substitute for full registration.
  

  Vehicles which cannot be issued a permit

  The following vehicles cannot be issued an Unregistered Vehicle Permit:
  
• Vehicles carrying a commercial load
• Vehicles exempt from registration
• Written-off vehicles (including vehicles written-off in NSW or interstate).

  Applying for an Unregistered Vehicle Permit

  You can apply for an Unregistered Vehicle Permit in person or by phone (provided you're already recorded in Roads and Maritime's systems).
  The cost for a permit includes the permit fee and CTP insurance. This CTP insurance only covers you on roads and road-related areas. It does not cover you on private property.
  You’ll be issued with a permit and a label. The permit shows the vehicle's conditions of use, and should be carried in the vehicle. The label or notice bearing the permit number must be clearly displayed on the vehicle when used on a road or road-related area.
  

  In person

  To apply for an Unregistered Vehicle Permit in person at any registry or service centre, you’ll need to provide:
  
• A completed Application for Unregistered Vehicle Permit
• Proof of your identity. If you’re registering the vehicle in the name of an organisation, you need to complete the Representative’s Authority section on the Application for Unregistered Vehicle Permit
• If you send someone else to register the vehicle in your name, you’ll need to complete the Representative’s Authority section on the Application for Unregistered Vehicle Permit, or provide a letter of authority. Your representative must also provide their own proof of identity 
• Important: If you’re not already recorded in Roads and Maritime systems, you cannot send a representative – you must attend in person
• A completed Vehicle Suitable for Safe Use Declaration form
• Payment for the permit fee and CTP insurance
• Number plates (if applicable).

  By phone

  If you’re already recorded in Roads and Maritime systems, you can request a permit by phoning 13 22 13.
  

Highlander
From this link http://www.rms.nsw.gov.au...tion/unregistered.html
 NSW permit looks easier and less messy than SA permit. Also valid for 28 days whereas SA appears to bhe only 3 days.

 

 
All of what highlander linked to and it has to be roadworthy. You can't go and collect a heap of *^%& and expect to drive it anywhere without getting stopped and red labelled. The friendly police will cancel your permit if its an unsafe car.