This is always a topic that bring out a number of answers. The agressive person always answers "As Much as I can". There are those that call all over town and expect to be paid "the going rate", and let's not forget our friends in the Union that have been setting standards for pay for years.
Our country has areas with different standards and different compensation needs. If you look at an apartment in New York City, and then look at the same thing in Atlanta or Dallas you would find the very same apartment renting for very different amounts. It is the same for fuel, and food and entertainment, if you move to different parts of the country the price of the same items change.