I take it your not on a package.. as i found the t/o transfer price quite acceptable, our only other trip was taxi i thought a fair price for the distance...

I've used the buses in the past, see below, allow a bit extra for the probable price rises.

http://www.holidaytruths.co.uk/viewtopic.php?p=554192#p554192

http://www.nerjatoday.com/bus.htm

Very easy to get to Nerja from the Airport. Catch the shuttle bus that goes from the airport to the bus station in Malaga and then their are about two an hour from the bus station to Nerja, it is almost as quick as a taxi but only costs a few euros and very straight forward. The bus company from the Malaga bus station is Alsina Graells and there is a web site so you can look up the times but they are frequent, and plenty of restaurants at the bus station that you can have some refreshment while you wait.