"This is a very rare, new, unopened one, and very hard to find." - it looks opened in the picture, or is that picture not of your cube?
Anyway I agree $125 (including shipping) is quite a bit high for an initial bid - if you started lower, maybe around $50 or even $20, you'd probably get a few people bidding on it and very possibly end up selling it for even more than $125.
Incidentally, there are not too many serious collectors here on speedsolving; I suggest advertising this on twistypuzzles.com (in the marketplace section of the forum) if you haven't already. Everyone there will know what a domino is and I'm sure there are quite a few people there with money to spare who will want to add one to their collection.