It was only available to authorized Nintendo developers, probably through the warioworld support site. Developer tools are always very expensive but you have to remember it's normally large companies that are buying them. They make profits back from the software they create, hopefully. The price doesn't reflect the general consumer market as it's not available for them to buy.
To get one of these you would probably have to know a DS developer that went bust or no longer works on DS titles, one that has a nitro capture sitting around and is happy to sell it.