In the last few days the taxi situation at Abu Dhabi airport has changed. You have to get a minibus now, which is metered and starts at 25 dirhams. A typical trip into the city will be approximately 100 dirhams at quiet times.
Hopefully the authorities will see sense and allow the normal taxis to pick up as well, otherwise they have to return to the city empty.
I am sure I am not along in thinking a bio 7 seater bus is a waste of resources for a lone traveller.