See this map? This is Mexico City's subway system. Each one of these lines, except the two on the far left, represents a grade-separated train with frequent service that costs the U.S. equivalent of $.30 for a one-way ride (this includes unlimited train transfers).
I've ridden these trains. They beat the pants off of everything in LA except the Red Line, but they go over a much wider part of the city.
How is this possible in a country with a much smaller economy than the U.S.? In the year 2000 Mexicans owned 189 vehicles per 1,000 people and people in the U.S. owned 771 vehicles per 1,000 people, the highest rate in the world (The High Cost of Free Parking, p. 679). When few people own vehicles, there are more people to support the transit system.
Want to know the craziest thing? They started building this in the late 1960s!