How much does it cost to get a tattoo?

This is an old debate, so the following is basic. You usually pay for work either by piece or by hour. The smaller pieces in the artist's flash book are "standard stock" material that usually don't take the artist too long to do. For these, you might find prices listed right next to the artwork. The artist may have a minimum charge that vary with each artist. Also, different tattoo kits the use charge will be different.
Large and/or custom pieces will usually be charged by the hour (unless you and the artist decide beforehand on the total price). If you get a "stock" piece (probably about 2" x 2" in size), you will probably not pay more than $100 and sit no longer than an hour in the chair.

If you bring your own design, the artist may charge anywhere from $50 to a few hundred dollars an hour. However, you may want to work with someone who charges $100 or so an hour; after all, you get what you pay for. Also, some artists charge for illustration time prior to beginning tattoo work. If they do, this might increase your price. If they tell you that your piece will be charged by the hour, ask them how many hours they think it'll take. Price negotiation should be up front and straightforward, a part of your initial discussion before work begins. Some shops take credit cards; most don't. Out-of-towners may be asked to put down a deposit. Be particularly wary of people willing to work "for cheap" or "for free".

Warning: Pay attention to the tattoo shop and its tattoo supplies, make sure the environment is clean and tattoo equipment are of high quality and sterilized. Then once the artist quotes you a price, it's final. The best way to get on the artist's bad side is to try to bargain with the price. If you think the price is too high, renegotiate the scope of the artwork, not the price. If you are very pleased with their work and service, you are strongly encouraged to tip the artist, even if they own the shop. Even shop owners don't pocket 100% of what they make (remember--it's a business!). Be prepared with cash on hand. I personally recommend a tip for any work which you are pleased with, or any custom work where the artist spent time drawing up your illustration (since drawing time is usually not included in your price). Nothing brightens up a day for the artist, or helps to build a friendly relationship with your artist more than a tip. If you're very happy with the artist and you think you might get more work from them later, tip.

There have been heated discussions on rec.arts.bodyart in the past regarding the appropriateness of tipping a shop owner. If you feel that an owner does not deserve a tip on top of the price they charge you, then do not tip, or bring some sort of offering. Many tattoo artists have told me that the best tip is good word of mouth. If you are happy with your tattoo, show it off to your friends and tell them where you got it done.