In an earth after nuclear war, a race of Lizards explores the desert for hidden cities, and artifacts that they can trade. One of these explorers is hired by a group of seekers (lead by a Human with a MAP, and followed by several men who are hired bullies.) The map points to a city, where for the last bunch of explorers the only survivor was an old pack pony. Good story.

: Is it worth the $40-50 most places are asking for it?

This is a novella length Trade size paper back published by Andre Norton Ltd. There are several states of this edition. The cover is white glossy paper, with a red drop of blood. I have seen copies where the red has run. If the copy is SIGNED and Numbered (ask about the RED CHOP - one of those Chinese name stamps) then it is probably worth the $40-50.
If the copy is not signed, or is missing the RED CHOP, it is a later copy, but if you don't have a copy it might be worth it anyway.
After the original signed/numbered copies were sold [red chop]; Andre Signed many of the rest of the copies for her charity.
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SERPENT'S TOOTH
Cover Chip Weston, il. by Mary Hanson-Roberts

1987, Andre Norton Ltd., Trade pap, signed and numbered 52p.
Limited to 999 copies total of signed and unsigned. $18.
[My copy as original: Signed by Andre Norton #346/975]
1987, Andre Norton Ltd., Trade pap, unsigned $13.00
signed and numbered 52p
Limited to 999 copies total of signed and unsigned.
[My copy as sold: later signed #285/975 but without Red Chop]
Yes, I have 2 copies. No, I'm not willing to sell one.