@MsClean - I'm so sorry to hear about your loss. You should consider yourself fortunate that your mother cared deeply enough for you to have left you with something so personal and so valuable as as a single cashmere shawl, let alone dozens of them.
Now to answer your questions. There really is no difference between cashmere and pashmina wool. Pashmina is actually the name of the Himalayan goat that the wool comes from. To put it simply, cashmere comes from the wool that the pashmina goat sheds naturally every spring.
Pashmina wool doesn't cost more than cashmere because as I've already mentioned, they are one in the same. However, the labels that pashmina wool manufacturers use when producing their textiles can be misleading.
The U.S. Federal Trade Commission does not recognize pashmina as a term for labeling products in the United States. When it comes to labeling garments made from the Himalayan goat, they must clearly state what percent is cashmere.
That doesn't mean that a shawl labeled seventy percent pashmina and thirty percent silk isn't a true pashmina wool shawl. It's just that the Wool Act does not recognize pashmina as a fiber because it's actually a type of goat.