You could use sub-summaries to show all the payment sources for the Projects.
Include all of your Project information in the top-part sub-summary sorted by your project primary key.
Your second sub-summary would be used to put your payment source information in sorted by how ever it relates to the project.
A summary report with sub summaries is the simplest to set up. If you really want these totals in columns on your report, it will take quite a bit more work on your part.
That type of report is usually called a 'cross tab' report. There are several different ways to create one in FileMaker using very different approaches. Most, however, have a fixed number of columns. The only option, short of exporting the data to another application, that i recall supports a variable number of columns (for a variable number of sources), would be to use the data to build an HTML table viewed in a WebViewer. If that's an approach that seems worth pursuing, you can search on "cross tab" in this forum and find posts that describe this method.