Hi,
It is not really rare. It was printed in 1946, yes, but it also contained other well known writers, so there would have been collectors of peole like Henry Miller and Sartre that would have bought these. Also, they printed 1000 of them, so if even 30% of them survived, that would leave 300 out there. Sompate that to the RARE book byu Bukowski "Genius of the Crowd" with an estimated 44 copies that were NOT destroyed by the Cleveland Police. If even 80% of those are still around, then there are only about 30 copoies of that book.
20 Tanks is the first piece, bibliographically #1, so there is that, but it is really a piece of paper.
Although I have seen values placed on this for much more, I have seen these sell for a couple hundred more than once, and these were for excellent condition pieces.
If I did not already have it, I would pay up to about $300 for it, but I'm a maniac.
When considering rarity/value, it is always best to consider the audience and supply/demand. If there is an item up for bid and two people with deep pockets both want it, the price goes up. If something is listed and no one will pay $600 for it, can it really be worth $600? Probably not. The value is only what people will pay for something.
Bill