I believe this chip to be pretty rare. I have only found a couple of pieces of info about it. One is a post started by Gene back in 2012. You can read it here:
http://www.thechipboard.com/archives/archives.pl/bid/322/md/read/id/1208516/sbj/dunes-hotel-and-bill-borland/

The only other thing I have found is a old ebay auction (not sure how old) where someone was trying to sell one for $109. I don't know if it sold
http://picclick.com/EDDIE-MILAN-DUNES-HOTEL-100-CASINO-CHIP-EXCELLENT-141014899707.html

I have two of these. One is on eBay, this is the other

Both sides shown

$25 shipped