I guess it is pretty hard to predict present costs with an oil price cut in half and therfore lower energy costs.
A company like Metanor is producing at 400 USD per ounce at most, even with a high oil price. Still, they don't attract buyers although they also had a set of very nice drilling results.
There is no rational right now. Just sellers, sellers, sellers and yes, some crazy buyer.
That crazy buyer will be able to buy half of Monaco or Cannes after a few years.