Valuing Rare Earth Companies

I have been making a serious effort to establishing a valuation model for rare earth companies so that I can compare the value of one company to another. It is not easy and explains why I have put the exercise off to the side for several years. However, the increasing number of rare earth explorers, developers, and even a couple of producers, has motivated me to now attempt to do so.
The difficulty with REE companies is that there are 20 or so different elements that can be produced and potentially sold from any ore deposit. One REE company has some elements while another has a different mix. Not only that, but the ore may contain elements that are not rare earths but have value (eg zirconium, tantalum, scandium and others).
On top of this:
a) the market pricing for a retail investor like me is a bit murky (ie hard to pin down or update easily)
b) companies report their REE in different ways. Sometimes they separate out the individual elements in their resources and sometimes not.
c) Most companies aim to produce concentrates but there are different kinds of concentrate
d) The range of elements in a concentrate vary, depending on the ore and so the value will vary, but how to determine this?

Probably, the most common statistic given is TREO, or Total Rare Earth Oxide. However, exactly which REOs are incorporated? Every company has a different mix. and each REO has a different market price. These prices vary substantially across the various elements.

Well, for me, this is an exercise in progress. Has it helped me value PEK? Maybe, but look down to my next post for this, because otherwise, the answer would be lost in all the words above.
Thanks for your patience