I took a taxi from LAS one time -- $18 one way between the airport and the Excalibur. It's one of the closest hotels!
After that trip, I decided that I would either rent a car or take the bus. One time I took the bus to the Crowne Plaza next to Hard Rock Cafe (a bus to the Strip requires a connection).
It's too bad they didn't build the train all the way to the airport. Then those scam artists known as taxi drivers could take a hike.