Cashmere comes in a range of weights from two-ply (which is tissue thin) to a eighteen-ply (think those thick hand-knit sweaters). The "ply" in this case means threads, so two-ply means two threads twisted together and then knitted; eighteen means just that: eighteen. That's not to say that two-ply is the cheap stuff nobody wants—it often makes for lighter sweaters perfect for layering under a jacket. The price does depend on the ply, but more importantly on the quality of the yarn. Lesser yarns, made from short fibers that break and pill easily, will certainly cost less. A quality piece of cashmere will cost you as little as $99 for Uniqlo's sought-after sweaters to upwards of a grand for Italian label Loro Piana.
Cashmere comes from the under down wool shed by goats in the Gobi Desert. It takes one goat four years to grow enough for one sweater.