Looking at the Holden web site the option for a full size spare alloy wheel and tyre is $350. Is this a price that is available when purchased after-market?
They only list full sets there though (4 wheels) and they go from about $1250 up to $2300, so they might be a little more pricey than $350 individually.
Best thing is to call Holden and see. I'd also keep an eye on eBay, and try a few wheel and tyre shops to see if they have one they'd do for a reasonable price. If it's just as a spare minor scratches and/or partially worn treads could mean you get a bargain.
Thanks for the link - very useful. I checked on ebay and found some but they're quite a lot more expensive considering they are used. Will give Holden a ring for a price on one.
Maybe the $350 for one is only at the time of sale.