I can get it to work with native fields, but it doesn't seem to work with a custom field. Maybe it's how my field was set up that I'm trying to compare (?) but it does appear to work for all native currency fields.
Switch to text mode and put in this for your actual cost fields. Then if you switch back to standard mode the bar will be highlighted, and it becomes a "picker", and you can select other fields to compare.
actualCost=FIELD:budget
actualCost_Mod=gt
