Psychologist can diagnose but can't prescribe medication: they do the behavior and talk therapy. A psychiatrist can diagnose and medicate, but usually don't do talk therapy, although some do.

Those two are the highest on the list of various professionals. I don't know how ur insurance is, but I see my psychologist 3x a week (15$/session). But that is really low I think. It can be anywhere up to 150+. I see my psychiatrist once every 6weeks for 30$. But that can also be 150+.

Ask about rates when u are interviewing. Some might be willing to work out a pay plan with you, if need be.