thank you for your comment! I have not sold any opal that I have, yet ;) I am considering another trip to Coober Peedy It was so much fun! I think its worth between $150 to $300.
It depends on how well it can be shaped and how deep the color goes.
I really love opal as well! I have been learning to grind them into cabochon.
It is a great skill and is relaxing!
Have a wonderful day!