Greyhound is not cheaper travelling from one well-served metropolis to another.

It *is* "generally" cheaper if you attempt to travel between two less-serviced cities.

For example, Reading, PA to Fresno, CA on October 1st.

The Greyhound fare is $250.

Travelocity and Expedia can't even come up with a routing, much less a price for a city-pair like that...