Anyone who says getting a tattoo doesn't hurt is a fucking liar. However, there are places that hurt more than others. Some hurt like a bitch, others just have a slight pain to them, but wherever you get them, they are certainly manageable otherwise you wouldn't have people who are extensively covered. I have 6, and aim to get more. I can confidently say that the one down my left forearm didn't hurt anywhere near as much as the one on my calf - that hurt like a fucker. My longest sitting so far has been 5 and half hours, with my shortest being 90mins. I have also used 5 artists so far.
Few pointers:
1) If you want a tattoo that badly, don't be fooled into thinking that a smaller one is a better choice. The pain should not be a deciding factor, as if you go for a smaller one to avoid the pain, you will inevitably want a bigger one once it is finished, so make sure that you are settled on the size you want it.
2) Do your research. Find a tattoo artist that you like the work of - do not be afraid to be ask for portfolios. Also, don't decide on an artist purely on price, many who get cheaper tattoos regret getting them because they are not as good as someone who charges more. Remember these things are on you for life so you have to like them.
3) Make sure that the studio is sterile and has an autoclave, as well as having seperate rooms, or at the very least areas, for the tattoos and the piercings.
4) Most artists will be happy to do a sitting of up to about 3 hours per piece (unless it's a big piece like a back piece or something where they can dedicate more time to it). Some will do more, some will do less. If you are really in that much discomfort *note I don't say pain*, then feel free to ask for a break, but remember that if you leave a session you will have a half finished piece of work on you...
Hope this helps.