Professional Associations are another good source for information – call the national office and ask if they do salary surveys.
You want to develop a RANGE for the position.
Then you want to check/confirm by talking with people in the field who are doing the kind of work you want to do (“My research indicates that salary range for this type of position is $ X – Y. Is that in the ballpark? High? Low?”).
Next add $ 5-10,000 to the range. Finally, you want to be sure you provide a range that you would be OK with. For example, if your research indicates a salary range of $ 30,000 to 70,000, and you would not take a job for less than $ 50,000, your range is $ 55,000-75,000.