WAX is my favorite method of transport when I stay at the south side of The Strip. You can catch it on the corner of Tropicana & Las Vegas Boulevard (in front of Tropicana hotel) to go back to the airport.
The fare is only $2!!!!!
It's a less than 10 minutes ride to go to the airport. The only downside is when you waited for it at the Tropicana's bus stop, there's only 2 seats available to sit on. You will most likely standing up and hope for it not to be late. Still, I'm a big fan of WAX.