There actually are more than two coding associations. However employers overwhelmingly want their coders to have certifications from the big two, so that is what is covered.
The Big 2
The two have a lot in common. A striking similarity is that they
both offer a lot of paid products. They offer certification exams, study guides, courses, books and CEUs. While it is not possible to avoid paying dues or buying tests and books (books can be bought many places), it is possible to pass the tests without buying other products.
About AHIMA
Founded in 1928 as a motion made and approved during an AMA meeting, AHIMA is older than AAPC. Even more impressive is that it's founding member (Grace Whiting Myers) basically defined and created the field of HIM. Her writings and career are worth a read. She was an interesting person.
There have been a few name changes through the decades. First it was the Association of Record Librarians of North America, in 1938 it was American Association of Medical Record Librarians. Then in 1970 American Medical Record Association before becoming AHIMA in 1991.
AHIMA is a not for profit organization.
There are six levels of membership. Group membership covers organizations. Costs are not listed on the site but presumably vary. Next is for members 65 and over followed by student. Both are $49.00 yearly. Global membership is $124.00 a year. One benefit of global is 5 free CEUs. Professional membership is $149.00. It also comes with 5 CEUs. Premier Professional level dues are $209.00 and one of it's benefits are 8 CEUS. This, and full membership benefits can be found HERE.
About AAPC
AAPC is sixty years younger than AHIMA. It began in 1988. Just like AHIMA, AAPC has also changed it's original name. Interestingly, it went from the American Academy of Professional Coders to AAPC (in 2011). Just AAPC. The initials no longer spell out anything.
Different from AHIMA, AAPC is a for profit organization. It's founder was Greg Lindberg (an interesting Google) and it's parent company is American Academy Holdings, LLC. Which recently bought Semantic Health. Unfortunately, I was not able to locate financial information.
There are three membership levels listed - student ($145.00) and Individual ($210.00). Membership comes with 4 free webinars and a free subscription to their monthly magazine which has a free CEU by quiz opportunity in each issue. This is accessible online. The third level is corporate membership, pricing not on the site.
A side-note here - In order to sit the AAPC exams you must be a member. Therefore it seems to make financial sense to get that membership before making any purchases from them. The price difference between non-member and member can be significant.