Hello my name is***** am a solicitor in NSW who will help with your inquiry today.
You can commence your legal action in the Magistrates Court of South Australia as a minor claim (I am assuming the difference in price was less than $25,000). Here is some information on how you go about representing yourself to do this kind of claim.
The basis upon which you can lodge your claim will be section 13 of the Sale of Goods Act 1895 which is here. That section makes it a condition of your contract that if the goods were to be sold by description (which it was, if you were told you were buying the 2012 model) then this is a condition of the contract between you and the vendor. Section 11 of the Act, which is here, lists a number of circumstances where the condition, if breached as it was in your case by the vendor, will become a warranty of the contract. You want this condition to be a warranty because you want the breach of it not to repudiate the contract (which would only give you a right to terminate and also damages) but you just want damages. So when you are preparing your claim form, you should cite both of these sections as the grounds for your claim. You should also cite section 52, which is here, and which gives you the right to claim the dimunition of the price or damages for the breach of warranty.
However, you should check the contract that you were issued by the dealer (vendor) at the time of sale, to see if there are any modifications to this, for example the situation may be that the contract excludes the legislative provision. The dealer may have done this in the contract but may not be allowed to do that, so you should seek further legal advice if your contract is like that.
I hope that has helped you with your inquiry. Good luck with your claim.