Piercings are priced first by the type of piercing: "clamp" (using forceps, such as a navel piercing) or the more difficult "freehand" (such as a septum); to which is added the cost of the jewelry. Within the minimum requirements for safety, you will usually have a choice of several gauges, styles, sizes, and materials for your jewelry. Most common piercings (including jewelry) run $50-$75.
In addition to the cost of the piercing and jewelry, you will need to invest $5-$10 for aftercare supplies, as specified in the aftercare instructions you receive.