How does the US afford to maintain its military presence?

I was recently reading about the size of the US military in comparison to other countries, and it got me wondering how they are able to afford it. The US has approximately 700 overseas bases with personnel from every branch of the military stationed in over 80 countries. Even if there are only 100 troops at each base, that is 70,000 troops. For simplicity sake, lets say 70,000 troops being stationed aboard at a rate of $50,000 a year (I think thats a low estimate). So thats a cost of 3.5 billion. Then there are all of the bases and personnel in the United States, its staggering that they can afford to maintain so many bases and have so many troops. I guess my question is how do they afford all of this? Just from taxes?