Alexandrite would be the color change stone. It will change to purple in the candescent light and in the natural light it will turn a bluish red. However if it is color changing and it changes those colors it is synthetic. Natural alexandrite will change from Red and green. The red and green is worth a lot of money. The synthetic still is collectible and desirable but it's a mix of sapphire and amethyst. If it is in Alexandria. Tomorrow morning go outside and see if it's a different color in the natural light.
Not highly valuable.... because there's so much of it available....
That said....
I just bought some rough Amethyst (ex Uruguay & Brazil).
You can see the rough prices, add another $45 for faceting 9like the middle Brazilian one and you can see that the stone alone COULD be worth up to $100.
That said there's also "artificial amethyst" where colors are enhanced by heating it etc - and if you search on - line you'll see that you can buy amethyst quite cheaply already faceted.
Given the setting etc it doesn't seem at all unreasonable...at the marked price!.
Value is only what someone will pay for it!.
Amethysts is a "birthstone" for people born in Feb - so very appropriate as a gift for women born in that month!