Corndog, whereabouts are you immigrating to? If you email me your snail mail address (Michelle@dirtrider.net), I'll send you out a couple of Kiwi magazines (Kiwi Rider & Motorcycle Trader). Why wouldn't you be able to get parts for the RMX? If you think we don't get them here, you're wrong. We get a lot of bikes that no one else does & all the usual ones.
KDX's new are $7995 or with a PC pipe & muffler $8500 (hope that's the right prices). GG200 are about $11,300 (I'm relying on my dodgy memory here), KTM's would be about the same. I'll find definite prices for you, if you like (but all the info will be in the magazines).
You don't need a licence or registration for trailrides/MX, only if you're taking it on adventure rides. A competition licence from MNZ is $80 a year, runs from June-June. Club memberships are around $20-$30 a year, depending on what club. You don't need to be a member for a lot of the rides, but some clubs do run rides where you need to be a club member (any MNZ-affiliated club will do), but offer a weekend membership (these are big events & huge fun).
If I can help further, yell out & I'll try. There is another member here who immigrated to NZ last year or year before, so maybe he can help, too. I'd have to track down his nick - he posts in the Euro forum.
Michelle