An entire back piece as your first tattoo?
That's gonna hurt like hell.
But if you really want to do it, research your local artists, see who's specializing in the style you want, and shop around. Not shop around as "find the lowest price", shop around to find a person you feel comfortable around, and who "gets" your idea. Then work with them for a while to formalize the design. If at any point before the needle goes in you don't feel right about them, bail.
Also, be prepared for several multi-hour sessions. And yeah, it's gonna be expensive. It should be expensive. You want the best, because it's permanent.