What you are describing is called a summary report.
Use part set up to add a sub summary part to your layout "when sorted by" your payment source field. You can set this to appear above or below the body layout part. If you then put the summary field that computes your grand total into this sub summary part, it will compute a sub total based on just the records grouped above or below your sub summary part. The records must be sorted by payment source or the sub summary part is not visible.
As a test, sort your records by track and then by payment source to group your records by track first, then by payment source. You should see the tracks that make up each payment source group and the total computed from them. Once you have this working, you can go back into layout mode and delete the body layout part so that you now only get one row of information for each payment source for a given track.