Well, if you want more-or-less meaningless statistics about an Open Source project, see https://www.openhub.net/p/moodle/, especially https://www.openhub.net/p/moodle/estimated_cost.
I think that is a bad guess, because it the Moodle source code contains a lot of third-party libraries not written by us, but the cost estimate is just done based on total lines-of-code count.