Hey Rich,
The only place on Oahu to pay for lessons is at Koko Marina BUT they aren't allowed to weight the boat down and they can't run a straight pattern due to the waters rules in that marina. So it's not the best place to ride on the island.
Will you be bringing your own gear? It would be best if you did. Contact my brother Reid (former owner of RNR surf & ski) at his email address -
hwpa@verizon.net, if for some reason he doesn't get back to you, email my private account and I'll put you in touch with some friends who ride at Keehi Lagoon on Oahu.
Etiquette is drop some cash for boat gas, bring your own food/drink or chip in extra cash for sharing with others, and help clean the boat after done riding because the entire boat needs to be soaped washed after because of the salt. If you can't stay to help clean up, it's customary to drop even a little more cash to make up for it.
Hope you have a great trip to Hawaii.