Welcome to CPF!
The R90 (9N bezel with N90 Lamp Assembly) is a hard to come by part in that it isn't listed on the internet that much.
The R95 (9AN bezel with N90 Lamp Assembly) must be about $100 at a guess.
The "holographic lens" is what SureFire call their BeamShaper. The BeamShaper for the 9N is the F34 (about $20)
Looks much like this:
The lens is frosted so that it gives a very even light for close range illumination (for paperwork etc)
Of course the FM14 BeamShaper also works on the 9N as well as the 9AN and M3 bezels. I prefer the FM to the F personally.
A thought just came to me(!)
If the 9N bezel has it's own frosted lens rather than a clear lens in much the same way as the F21 Bezel, then I do not know the part code for it and in fact I have never heard of such a thing. It's value to a collector could be quite a lot.
It would be useful to know some more details of the part you have.
Thanks!
Al