I don't know if this will help, but I too am hoping to find out because I recently (the past 4 days) purchased a moonstone bead necklace from vendor search for 175m. I have never saw one of these ever, nor heard of them. I was told that they used to sell for 50m, and that they are farm-able from the cook still as well since then... but nobody knows the price now it seems.
Apparently they are pretty time consuming to get, but I have not tried it myself. The only posts I can find mention someone offering 20m 9 years ago or so. And there are a few other posts about players farming / trying to collect them. I could not find a single post with one having actually been sold / bought ever. (I saw the Raresfest post, but that doesn't count.)
If anyone knows an accurate value, please let us know. I think it's much the better to not buy any of these until someone finds out, especially for 175... I may have jumped too soon on that. Hope not, but lesson learned.