We have taken O air but pay the deviation ($175 PP to deviate pre & post cruise ) one time fee unless you change your mind after you paid the fee
We ask for the flights we want on the days we want then see if Oceania can get them within their contracts with the airline
Once they wanted an upcharge we declined & looked for other flights
You only pay the non refundable fee once you & Oceania have come to an agreement on the flights
If you do not live near their gateway cities then there may be a charge from your local airport to a gateway
We live near a gateway city YYZ so no problem for us
Option 2 which we do more often is to take the cruise only fare & book our own air especially when we do BIZ class