The cost of Duncans is variable and all depends on the color. Most of the really bright, neon green Duncans if they are the ORA variety sell for $50-$70 per polyp. The tanish or dull green Duncans can be purchased for $10-$15 per polyp. It the same as having a brown acro vs a tri-color acro, it's all relative to the color and what the buyer is willing to pay.
It's a shame to bust up a show piece like that one, maybe contact a local Aquarium, if you have one, if not maybe try some of the larger ones outside of your area. Not sure who you would call, maybe the curator?
Better yet, why not just keep it and let it continue to grow!