Odds of Getting In
As far as breaking into the biz of music therapy, it's not like there's an overabundance of music therapists out there vying for the same position like, say, actors or professional football players.
Getting a job as a music therapist is difficult in that it takes some educational commitment (which takes time and money) and finding a good mentor for your internship. See, although it's not a new type of therapy (again, we must reference Lionel Logue, whose therapy was invaluable to King George VI) it is a fairly new career in and of itself (meaning just music therapy, and not music therapy combined with other, more traditional therapies).
Very few schools and hospitals have in-house music therapists and it's up to you to convince them that your services are needed. So be prepared to show some case studies and then win them over with your amazing credentials, recommendations, and dazzling personality.