You do not have to have a degree to be a medical coder. However, if you want to improve your chances of getting hired, then get certified through either AAPC or AHIMA. Many of the job postings for coding jobs list a particular certification as a requirement along with being a high school graduate. Certification shows that you have committed yourself to become knowledgeable in the field of medical coding.
CodingCertificaion.Org offers an AAPC approved 80 hour course that will prepare you for the CPC exam. It can also help you prepare for AHIMA's CSS certification. Here is a link to info about this course:
Physician Based Medical Coding Course
I have recently completed this course, myself, and subsequently became certified as a CPC-A. I liked the course because I could go at my own pace, was well organized, and the materials were up-to-date. The assignments give you lots of practice and when you have questions, my coach, Alicia Scott would explain what I needed to understand.