"The Guide" publishes wholesale gemstone prices in the US which you can subscribe to at US$195 a year. Their website is www.gemguide.com. It gives a very comprehensive price range for most commercially important gemstones, differentiating between gemstone quality, color varieties, sizes and in some cases, gemstone origin.
This is useful if you are able to grade gemstones somewhat competently, ie. if you can tell the difference between a commercial, good, fine and extra fine stone, you will be able to get a rough idea of the price range. Even so, the range can be very wide. For eg. Good quality Tsavorite under 1 ct ranges from 160-300 per carat. Extra-fine Blue Sapphire between 4-6cts ranges from 6000-8000 per carat.
In reality, stone pricing is subjective.
Unlike Diamonds, colored gemstones are not graded using a universal grading system. While everyone wants a Diamond that is white and bright, it is not so for the colored stone market. Take for example Ruby. The market ideal is pure red. However, Japanese love their pinkish red. So while a pinkish-red Ruby might be worth $200 in Japan, it may only sell for $150 in the US, where they are less desired.
Furthermore, unlike Diamonds, there isn't a single channel distribution system for colored gemstones so prices can really vary from place to place.
Do gemstone prices fluctuate like gold and silver? Due to its lack of liquidity, the answer is no. The prices rise and fall like any other commodity but you won't see anything as dramatic as gold!
Hope that answers your questions!
I LOVE gemstones and am a gemologist.