def cost_validation(money):
    """ Decide if the money input is valid.

        Parameters:
            money(str): A user's input to the cost question.

        Return:
            (str): A single valid string, such as "$" or "$$" or "$$$".
    """
    while money != "$$$" and money != "$$" and money != "$" :
         print("\nI'm sorry, but " + money + " is not a valid choice. Please try again.")
         money = input("\nWhat is money to you?"
              + "\n  $$$) No object"
              + "\n  $$) Spendable, so long as I get value from doing so"
              + "\n  $) Extremely important; I want to spend as little as possible"
              + "\n> ")
    return money