According the Professional Guide to Gemstone Values, as of March 2014, amethysts are worth between $7.00 and $70.00, depending on color and carat weight. In general, the darker the color, the higher the value.
According to the guide, the most valuable amethysts are those that are categorized as "medium reddish purple with a slight tint of brown." This rare amethyst commanded between $64.00 and $70.00 as of March 2014. At the same time, the least valuable amethysts were those that were "very light purple" in color. This type of amethyst is common and commanded prices of less than $10 for a 1-carat stone.