Salary
Average Salary: $68,900
Expected Lifetime Earnings: $2,876,437
Clinical therapists, counselors, school psychologists, and family therapists make an average salary of $74,000 (source). However, an average salary for an art therapist is more like $40,000 (source).
Considering you need the same schooling (i.e. rack up the same student loans) and get the same license, you may want to hold the title of counselor or family therapist who uses art therapy in his or her practice.
You'll be able to take all of the same sorts of patients that any other therapist would, you'll just specialize in using art therapy techniques on them. You can even get a special art therapy license from the Art Therapy Credentialing Board, so long as you take the requisite art therapy courses and get a related degree.
One of the best options to consider if you want to practice art therapy is to get a degree in counseling with a specialty in art therapy, then get credentialed by the art therapy board. After that, you can get a job working at a hospital in an elder care or pediatric care unit. You could make about $82,000 doing what you love.