My knowledge comes from shipping a bike one way and substantially further, so other people will know more about return trips, providing your own crate rather than having the shippers provide one, and whether an insurance green card will cover risks at sea (I was surprised how much insurance came to, but ships can sink...)
Using a good "handle everything" shipping service, I'd guess the return trip cost might get into four figures but all you'll have to do is hand them the bike with the tank as empty as conveniently possible then collect it at the other end. And I'd think that the bike would be in transit for a month or so in each direction - be aware that time taken consolidating your crate into a container of part loads until it's full and on a ship needs to be accounted for so that you don't spend your holiday waiting for the bike.
All I know about air freight is that a bicycle was pretty expensive, and weight was a major consideration...
