Far be it from me to add much to the discussion, but I might interpret
your question a little differently....
Have you tried to show the summary task? On the Gantt Chart view, go
to Tools > Options > View, and select the Show Project Summary Task
checkbox in the bottom right.
Close out of there, and make sure the Cost (or Actual Cost - kinda
hard to say) field is showing on the Gantt Chart. Right click in the
top, and insert the appropriate field. I think you want Actual Cost -
which will show incurred costs to date. Cost will show you the
current estimate for the entire project cost as of today (including
estimates of future costs).
-A