We used EZ Air last month to fly round trip from SFO to Auckland. You can deviate the flight to add extra days on at the beginning, or end, of your cruise. You pick from the flights offered, so you have complete control there.
We will use EZ Air again in September. We have one way flights, on Air Canada, from Sacramento to Barcelona. The cost was $550, per person. I haven’t been able to find anything cheaper.