Officiants vary as to services that they offer. In general, most will include a full formal ceremony, a rehearsal along with signing the license, and coordinating the flow of the service. Some offer celebrations that have no rehearsal for less, and as well a quickie ceremony for elopements.
What a couple pays tends to be determined by where they live. For example, fees in California, New York, and other cities might be higher than ones in smaller towns. The best advice I can give is to look for an Officiant that is professional, polished, and well versed in what they do. In this case, you want the best person for your job. Your wedding is a once in a lifetime affair. Consider that cost should not be your priority. The right Officiant can make or break the most important day in your life.