What is a substitute drug that is cheaper than agrylin (anagrelide)?

None I know of: As far as I can tell, Agrylin is the only available form of the drug anagrelide. There are other options, but only your hematologist can tell you if they are appropriate for you, and I don't know whether they are cheaper or not. The oldest drug for this is Hydroxyurea which is often combined with aspirin. If you cannot afford drugs, the companies do have vouchers; check out Medicaid and/or ACA.