Botox is currently approved for wrinkles in the face,
Allergen has applied for approval (clearance) for sweating among other indications. I would go see a plastics guy and ask him about injections in the arm pit, may help may not,
Allergen customer service could probably help you answer that question, plus if they are still in clinical trials you could get free injections.
I have had Botox injections in my forehead at least 10 times over the past 6 or 7 years.
Initially it lasted for about 6 months, but progressively it lasted longer, up to 10 months.
I have paid 500 all the way down to free injections. So pricing is varied, I believe it has dropped considerably in the past few years.