A vial of Botox cost all physicians about the same and contains 100 units of Botox. The vial comes as a dry power which is reconstituted with sterile saline. Different providers use different amounts of saline. This is usually anywhere from 1-4ccs. This means you could be getting anywhere from 25 to 100 units of Botox per cc if you paying buy the cc.
Studies suggest that the higher potencies (i.e. less dilute) of either 1-2ccs tend to work the best. Botox should normally cost between $10 – $18 per unit, depending on the injector. Any less and the Botox is most likely from outside the country which is both illegal (The FDA cannot monitor it) and highly suspect for counterfeit. If you buy it by the unit, you understand exactly how much your provider is using over which areas and make sure you get a fair price.