Botox is sold to Physicians in a 100 unit vial, not by syringe; Botox is reconstituted with saline by the Physician with 2-2.5 mL depending on preference. The cost to the Physician for this US FDA approved vial is around $550. Although Botox can be priced per area, my preference is to sell it by the unit. The reason is that Botox is a medication, with some patients requiring more and some less. Cost per unit will depend on where you live, but in my practice it is $13/u. Because Botox is used heavily for therapeutic reasons in the United States, Botox cosmetic must be sold to the Physician at the same price as Botox intended for insurance/ Medicare purposes. Therefore, there is no volume discounting of product for the Physician, as there is with competitors such as Dysport or Xeomin. Therefore, if you see heavily discounted Botox, Botox offered by the "syringe", I would be suspicious of the origin, quality, dilution, and integrity of the product.
Web reference: http://www.drprendiville.com/facialcosmetic-nonsurgical.html