I found this pic, showing how they used to be sold, in sets of six. Can't see the threads, but otherwise these appear identical to the ones I have. (Sorry about the glare -- there are as many crappy photographers as there are cameras, I think.)
is a guy trying to sell 24 of these for $260 plus freight.
I think I'll just put six of 'em up for bids on eBay, maybe start 'em at $30/set and see what I get.