Though never really a 'star' until the post-Godfather years...Robert Duvall had enjoyed steady work as a film actor throughout the 60's in many character roles since his 1962 debut in 'To Kill A Mockingbird'...even co-starring with Brando in at least one Western.

That might explain his ever so slightly higher salary and paid expenses as opposed to Pacino/Can/Keaton who in comparisson were really at the beginning of their careers.

Apple