http://www.stuff.co.nz/motoring/customs ... for-46-000
The cool factor and nostalgia for especially split buses means that the market is apparently insatiable. They aren't making any more of them, but we keep making more people. As long as it's legal to drive vintage cars and as long as people who weren't even born when they were made still want them, prices will only go one way.
Those who blame rising prices on sellers' greed should note that this bus sold at auction; the prospective buyers determined the price. This was not one of those Barrett-Jackson pissing contests in the US, where obscenely wealthy buyers throw ridiculous money at often poorly restored split buses and other classics just because they can and they want everyone to know it.