If you are going to military route, you pay in years of service. For the Air Force, you are committed to serving for 10 years after you graduate pilot training.
For civilian, you are paying for yourself (unless you found a sweet scholarship). This can be fairly expensive. Price depends on how far you want to take the training. Your initial private pilots license will be about $8,000-10,000. If you want to make being a pilot your career, you will need an instrument rating, a commercial license, and many many hours, which will add up to a bit.
If you just want a private pilot license for fun, then go for it! If you are looking to make a career of being a pilot, I highly recommend the military route. Serving your country is a great way to spend your life. And it also is cheaper!