The cheapest I have seen them is $50 a polyp. A auction just closed a week ago on the famous site. One polyp went for $227.
I hope my little frag grows out fast so I can make a little back before they are selling for $10 a polyp. I have only had mine for a couple weeks and already have about 3 new babies on it. The guy I got them from said he grew 18 polyps in 6 months. Here is a pic.