What price does Thorin place on the Arkenstone?

Thorin doesn't place an exact price on the Arkenstone, as it is priceless. 

"For the Arkenstone of my father," he said, "is worth more than a river of gold in itself, and to me it is beyond price. That stone of all the treasure I name unto myself, and I will be avenged on anyone who finds it and withholds it."