They range from £400 to £1000 depending on condition. That one looks like one of the rarer blue vinyl covered ones (they did black, blue, beige and brown) and it looks like the vinyl is loose on the c pillars, very common, and generally unrepairable. The inside in comparison is easy to fix, see my mini blog on it.
http://www.e30zone.net/modules.php?name ... headlining
Shipping to NZ is an ablsolute fortune, so if you fancy a hardtop, get that on bought! If its a nice car, and you haggle well, who knows, it might come for free on buy/sell of the car?
As Daimlerman says, painting it is a lot of work. I'd first clean the hardtop with something like AutoGlym engine and machine cleaner, scrubbing the vinyl really well, rinse thoroughly, then treat with something like AutoGlym tyre preparation, you'll be surprised how good the top then looks.
If painting, use as little primer/filler as you can. The hardtop really strengthens the car, but of course then has to absorb all the shakes between front/rear, so if you use think paint/filler etc, it will crack. Ive always thought that BMW chose vinyl so that it could achieve the BMW look on the hardtop, without the stress problems that fibreglass has. Wiesmann were able to achieve the painted look by using curves in construction, but is a much heavier product in comparison.