According to THIS WEB SITE, the poster below was in North Korea's Koryo Museum. The poster says that a female slave between fifteen and fifty years old once cost 120 pil (120필) while a male slave of the same age cost only 100 pil. Female slaves under fifteen and over fifty cost sixty pil while males slaves in the same age brackets cost only fifty pil. If you had the money, you could have gotten a cow for 400 pil.
Matt also has a link to a better picture on HIS SITE.