Rob, something like this. 335/30/18's on a Harrison.
Don't limit yourself to Pirelli. You can get some really good deals from US Viper dealers on 335/30/18 Michelins. I bought mine from a Viper dealer through eBay US. They were very, very cheap, brand new with sticker on the tread. From memory around AU$350ea landed. Just make sure you shop around and are patient.