Cost per unit: Amount of botox is measured in units. It comes in vial and each vial contains 100 units of botox. The quantity that is required for the treatment is measured in units. The units of botox required for the treatment of excessive sweating in each armpit depends on the severity of condition. Some dermatologists charge for the botox treatment on the basis of units of botox used. The number of units required lies between 80 and 150 and the average cost of botox can be somewhere between $10 and $16.