How expensive are these schools?

I am really interested in a career in medical billing. However, I am not sure whether I can afford the training that is required for this. Can anyone tell me whether there is an inexpensive school for medical billing online? I really prefer to study online so that I can spend less time and choose the time that I do my studying. I am hoping that I can find a good program soon and get started learning how to do my new career. Hopefully it won’t take me too long to complete the program, but as long as it is affordable I am interested.