The most valuable jade is high grade (A or AAA) jadeite with glwing translucence and vibrant emerald green. Jadeite in this caliber is used for jewelry and cut "en cabochon" or made into a bead. Jade like this can range from hundred into millions of dollars. The lowest grade of jade may be a dyed nephrite of poor quality and can be found on a necklace for a few dollars. Jade can range from a few dollars to millions. You can find more information here: http://www.shopgemstones.com/value-of-jade.html
How much jade is worth really depends on the quality of the stone, whether or not it has been carved and the age of the stone itself. Some pieces of jade are not pure and are not worth very much at all but very old pieces that are intricately carved are valued at over a million.