2002 and 2003 Penfolds grange magnum $899 from Jacks Wine
$899 is a hell of a bargain given that the standard price for the same two vintages is $1699 although I've seen it as high as $1999 and low as $1399. Its just over half the standard price and pretty much a bogof.
From what I can make out the 2002 will be the better buy. Its consistently held its price and seems to be closer to being sold out. The projected shelf life of the magnums is 50 years, longer than the 750ml. There are less than 1000 of them bottled each year and each is individually numbered.
You literally could buy 2 put one on the market through auction and get most of the cost of the bottle your keeping back. Your also pretty much guaranteed that the wine will nearly index itself to inflation so given the discount your purchasing it at you'll be way ahead if you keep it. From the prices I've looked at only one year seems to have bombed in price - all the rest have increased. The 1998 magnums are currently going for around $2500 at auction.
They're not selling this online so you'll need to call them up on the number at the bottom of the newsletter on the go to deal link - and of course cashback wont apply given that its not being completed online.