The costing I have on moodle.com was based on these features listed here: http://moodle.org/mod/forum/discuss.php?d=1746 ... ie:
- support for more browsers including screen readers, lynx, non-javascript etc
- support for server-based daemon for larger installations
- nicer interface for inserting pictures etc
- integration of drawboard for collaborative drawing
- help pages (and buttons)
(See also a related discussion about funding methods in general here: http://moodle.org/mod/forum/discuss.php?d=1848)