Remember that humans weigh 10-20 times as much as a cat, so it's likely that ANY human supplement will be WAY too high a dose for a cat. Too much of even a good thing can be poisonous to your cat. (Imagine if you took 20 iron pills all at once.)
While it may cost more, you need to consult your vet and go with what they say to do. Ask them for less expensive options, if that is an issue.
And "anemia" is a generalized term, so as the others have said above, you need to find out what kind, why, and how to treat the whole problem correctly.