There are different services in Hawaii for Honolulu airport transportation to Waikiki. The cheapest of these is public transport via TheBus. As in all other states, public transport is a favorable means to travel if you wish to spend the least amount of money.
From Honolulu Airport, you can take buses No. 19, 20, and 31. The route number 19 passes through Kalihi Kai, downtown Honolulu, the Honolulu Civic Center, Ala Moana Shopping Center, and finally, Waikiki. Meanwhile, route number 20 gives you a ride through the Arizona Memorial, Aloha Stadium, Aiea, and finally, Pearlridge Shopping Center. Route no. 31 has a direct path through Kalihi Transit Center.
Bus rides are an apt choice for traveling to/from Daniel K. Inouye International Airport. If you have limited luggage and can compromise with your schedule a bit, bus rides are an okay option for traveling to Waikiki and across the island.