We can in do it in this way. first creat a list report in which u have a calculated item in the starting.

Then creat a prompt page with a value prompt.In value prompt creat static choice of which u want to be dynamically displayed.

Let the parameter of value prompt be ?Par1? and the choices as Revenue, Cost.

Now u write the expression of the calculated item in the report page as follows, "If ?Par1?=Revenue then Revenue else Cost.

Here Revenue,Cost should b dragged from the Model Items. So now the calculated item column displays the value of the one selected in the prompt.

Now make a graph using the list report,then place the calculated item on the axis of the chart ,which u wanted to display dynamically based on ur selection.

So now if u select Revenue in the prompt then the grph will take the values for Revenue.And if u select Cost then graph will be with the values of Cost.

Let me know wether this is working good r not,for my confirmation.