You'll save money that way as your flight instructor won't need to spend so much time going over the material you need to know right away. The things you learn in ground school will definitely be needed as you learn to fly. However, most people require a bit more than that. The average is around 60 hours total. It is possible to do it in less time though if you fly frequently.
Prices vary for the airplane and for instructors.
Normally you are charged by time on a meter in the airplane called a Hobbs meter. It clicks off tenths of hours only when the engine is running. Again, this is just an estimate and your cost may vary. Most people train over a six to twelve month period. Flying is a physical skill as well as a mental skill.