Botox for the underarms needs to be injected every 3 to 6 months and is very individual in its longevity. I try to get a health care insurer to pay for it as hyperhidrosis is considered a medical problem.
Remember that since most insurers make you jump through hoops before they pay for surgical sympathectomy, and require treatment with Botox, they must consider paying for such treatment(s).
Depending on how large your underarms are, they can require between 80 units and 150 units at a cost of 10 dollars per unit.
I also perform miraDry and this is an option for those who can afford to pay out of pocket for this procedure. It is FDA approved for underarm sweating.