Ian McKellen (Gandalf) recieved �4,000,000 for "The Fellowship of the Ring". He recieved �5,000,000 for "The Two Towers".
Again, from imdb. Sorry I couldn't find the other actors salaries, but you can imagine that Viggo Mortensen (Aragon) and Elijah Wood (Frodo) also earned around the same amount. Christopher Lee (Saruman) probably unearned less than half that, and the other Hobbits, slightly less than that.
I do not think the amount of onscreen time DIRECTLY correlates to how much they earned. It's also how high their profile is. Ian McKellen, Christopher Lee, and maybe Liv Tyler, have quite high recognition compared to the Hobbits and other members of the Fellowship.
Hope I was of some help. By the way, why were you interested in this information?