Merry Meet Bo Liao,
Although there is a probability its fake however its not because of
the monetary value you paid for it. For the price you paid although
you can't get a really good one however its enough for a moderately
NEW DZI.
Real or Fake? The difference lies in the Material used & the
Etchings. Mostly Fakes are made of Glass, Plastic & other
synthetic materials & of coz they don't radiate much vibration
at all. Even Real DZI beads there are grading whether its a NEW or
OLD Bead, Low grade, Medium grade, High grade or Super grade, these
Relics are just like precious stones. Slight difference can make
vast difference in its monetary value. Well its hard for a layman
to see the difference but with a reliable source & if you are
sensitive to energy, you can easily tell a difference between NEW
& OLD Beads with the explanation of the owner.
Well the perspective you have about dZi beads is what many others
may have. Fake dZi beads are made of synthetic medium & they
are not all Dirt Cheap some can be sold for a nifty sum by
Unscrupulous Seller which did happen before as we can see in
Newspapers, definitely they do not emit any vibration as the
Authentic ones do in term of Spiritual Aspects. In term of
Gemological Aspect, they will definitely fail as Authentic dZi is
of Natural Rocks & Minerals. In term of Value, dZi is an
Ancient Relic, a piece of History sought after by collectors of coz
that relies on whether its a NEW or OLD Bead.
Hope all these answer your queries.

Blessed Be,
Oceanos