Tattoo pain, length of time, and cost?

I'm only 15, but my mom said she would let me get a tattoo. Because I adore snakes, I want a coiled snake that takes up the length of my shoulder blade and goes to the neckline. How painful is it to get a tattoo on the shoulder blade? How long do you think it would take? That tattoo is in black and white, pretty much, but has some scale design on the snake and is shaded to look almost 3D. Also, if I got a reputable artist to do it, how much do you think it would cost? Thank you