YIKES...that's just crazy! About 40 years ago, you could buy a color changing, flawless, 2 carat stone, set in silver, for less than $50!
I think you're thinking of another stone....
or maybe the big fakes that have been around forever....I've been a collector for a long time, and I've seen lots of the big fakes (I've got a nice doorknob) but finding a real one of decent size and colorchange is damn near impossible.
Real alexandrite has never been plentiful and it's never been cheap. Seriously, I have a tiny quarter carat that I got years ago and it was appraised as authentic.
Maybe you're thinking of the color change topazs or garnets?