I have half sleeve on my left arm, took about 7 hours (done in 3 stages over the course of around a month) and cost me roughly £200. I was incredibly lucky to find an artist who was both good, and inspired enough by the project that she didn't want to charge too much and therefore put me off
Heather Moore at Evolution Skin Studios in Canterbury is the lass who did it. Her boss, Helen Porter, is extremly good at tribal work and does alot of big pieces. Cant really tell you her average prices, but she's worth a look. Here's Helen's gallery: http://www.pink-ink-tattoos.com/gallery/index.php They charge by the hour, usually between £60 and £80 depending.
My only real problem with my tattoo is the fact that people, complete strangers, will not stop lifting up my sleeve to look or jabbing at my arm. And the questions x_x "Oooh, I bet that hurt?" and so on, get really annoying. I'm lucky enough to work in a metal/rocker bar, so there's no problem with displaying my tattoo's at work. It's mostly just the people that get annoying.
If you're going with tribal, get them to design something bespoke, ask for influences from an actual Tribe (Hawaiian tribal tattoo's, for example), and maybe try getting a small part of your arm done first - somewhere on your shoulder. You can then make sure you actually like the design, like tribal, like having a tattoo that is permanant, and get a rough idea of the pain and process's involved etc. Alot of places (the good ones) will not do a full sleeve/other big piece if it is your first tattoo.
Also consider get it done in small stages. A shoulder piece moving to a half sleeve, moving to a rough 3/4's and so on. Getting comfortable with and taking care of that much ink in one go is extremely difficult, so smaller sections help. Research the tattoo parlours around you, and look at old designs. Ask for something original, and see if they can include shapes or tribal-based images that mean something to you/that you can use to aid memory of certain events or people.