Hi Jenny,
What you can try and do is create a brand new formula coloumn and put the Cost YTD formula in it. Then publish it to a perspective and lock it to a specific object (Business Services or Business Units). Then pull it in to the new report component you are trying to make. Sometimes doing the configuration that way can work because it forces the formula to look at only that object.
Let me know if you have any questions,
Lauren Griessel