What is the cost of a taxi from the Honolulu Airport to Waikiki?
When I visited Honolulu in mid-2013, I took a taxi from the Honolulu airport to Waikiki and paid about $45.00, not including tip. It took about 20 minutes to reach the main strip of Waikiki (where all the hotels are) from the airport.
Alternative to taxi from Honolulu airport to Waikiki
I strongly recommend that you use a shuttle service called Hawaii 23, because they only charge $23 for a shuttle from the airport to Waikiki or the other way around, for up to 3 people. It’s obviously much cheaper, and they’re a great company.