Agree 100% about the posts advocating the public bus - just remember to ask "Directo" otherwise you will stop in Alaluala - not the end of the world - I've got lots of trips and travel light, night or day the public bus is the best option for me. With the taxi to my hotel and the bus fare its less than $3.00 vs $20 - 30 for a taxi and +/- $15 with Interbus w/ a small tip - lately I'm hating all but the public bus....
OTOH.....
If you see some like minded folks at the airport, ask them if they are going downtown (they don't have to be going to your hotel; does not matter) and see if you can share a cab - 3 sharing is ideal but 2 works too.
The taxi rates have really increased over the past few years - you still should be able to negociate a one way for $20.