How Expensive is It to Go to a Prom?

I am just get ready to do the math on this, because I have twin daughters. Both of them are extremely lovely girls and both of them have been invited to the prom, even though it will not be for another month and a half. They have been showing me pictures of prom dresses for 2013 and I can not say that I am overly impressed by the prices that I was shown. They seemed to like all of the most expensive types that you could possibly buy. Then they started talking about everything else. I laughed at them for talking about limousines, even though they thought it was very reasonable for me to split the cost with the parents of their dates.