It is a very nice piece, and these things used to be all the rage years ago... $100 is more than fair for it!
However, at 12" you will only find a home for it in a large tank. And that limits your customer base. If I had my big tank up and running, that would be a great fit. However, I only have a 75g for a display, and real estate is minimal.
You may get better results if you frag it up and sell it as smaller pieces. You might even make double what you would selling it as one big show piece.