I have not tried it or seen it, but it appears to most likely be
glass, which has had some metallic sputtering done on it to produce
the “color change” of alexandrite. So I would guess that, provided
they really are as described, the price is probably fair. Although I
have seen “dime store” jewelry (my Mom has a piece that predates the
appearance of alexandrite!) with the same general effect, probably
for less money.
Margaret