Thorium is a by-product of mining heavy metals and rare earth metals. The price is the cost of extracting and refining, which can be as low as $40/Kg. No extra mining is required for extracting the Thorium, and we all know that mining is a major source for pollution.
The first thing we must realize is that rare earth metals are not all that rare. They are a thousand times or more abundant than gold or platinum in the earth crust and easy to mine, but a little more difficult to refine. Thorium and Uranium will be mined together with rare earth metals.
U.S. used to be the major supplier for rare earth metals, which was fine up to around 1984. Then the U.S. regulators determined that Uranium and Thorium contained in the ore made the ore radioactive, so they decided to make rare metal ore a “ground source” with all what that meant for record keeping and control. This made mining in the U.S. unprofitable so in 2001 the last mine closed down. China had no such scruples, so they took over the rare earth metal concession and in 2010 controlled over 95% of the world supply, which was right according to their long term plan of controlling the world by 2025. Luckily this has now been rectified with U.S. and Australian mines reopened.
So, why is this important? Just take a look at all the uses for rare earth metals. The most sought after pays all the cost of mining and refining, and the rest are readily available at nominal cost.
The Chinese almost got away with it, and that is but one reason the trade negotiations are so complicated and hard fought, but necessary. Donald Trump fights for reciprocity and fair competition.