Why just Top 20 schools?
I agree that I can’t think there is much you can do to strengthen ECs while you are serving in your country Army. But that seems like a strong thing to be adding…although I suspect this is a requirement. Am I correct?
What can you do to get accepted to an affordable college in the U.S? You need to broaden your search to include places where you WOULD receive significant merit aid.
There are many many colleges in the U.S. where you can major in economics/business/math.
What is your career goal, and where do you plan to work. After undergrad, it’s highly likely you will be required to return to your home country.