Somebody upstream mentioned Uber; this is still not legal in Vegas. In fact state senate just voted it down earlier this week.
One thing I did once is head to departures, and I jumped in a cab dropping someone off. This is illegal for the cabs, so they won't do it if you have a lot of bags to load, but if you just have a small carryon and are quick you might be successful. It also depends on how busy drop off is.