Employers will often pay higher wages to entice workers to accept positions with unpleasant aspects , such as midnight shifts, dangerous work, etc.
Wages will often differ based on the cost of living in different cities; for example, the cost of living in California is higher than the cost of living in Indiana, so wages in general in California will be higher than those in Indiana.
Opportunity Cost - The value of any alternative that you give up when you buy something else or make another choice
Example: You want the 2010 Madden football video game and concert tickets to Dave Mathews Band. You chose the video game. Part of the “cost” of the video game is now you don’t have enough money to go to the concert. That is your opportunity cost.