I bought mine from Eden Tack and Tails in BC. I think they are $399 Canadian now (plus shipping but that was reasonable)! They were great to deal with and I highly reccommend them based on my experience!
I have been going through an issue with mine (bought them in Feb and in May the first time I really used them, they stopped working) and am sooooo much happier now that Ed from Eden tack is who is helping me get a replacement motor so I don't have to deal directly with Double K anymore as their customer service, in my experience, was absolutely the pits!!! :arg! If I didn't really like the white knight shampoo, I don't think that I would buy another Double K product!!