I shot a Wisner/Polaroid 20 x 24 almost 2 years ago. (there's ONE picture in my gallery here from it). One travelled to Florida for Fotofusion or some show like that and stopped at a local community college. I rented it then. It wasn't cheap, but it was worth it. Although, it was cheaper there than it would've been flying out to rent it.
There's actually about 14 cameras now, whereas there used to be only 5. Since Wisner is making them now, they are starting to pop-up again.
My good friend Barbra Oosting recently purchased one, it's the camera she uses for her art and will save her money in the long run.
She won't have to travel to San Fran and use Tracy Storer's camera anymore. By the way, he's a really nice guy!
They are pretty expensive. When it's all said and done, you will be spending about 30,000 grand between the lenses, processing back, camera, stand, etc.