By Boat : count 4000 euros, for example from Le Havre to Melbourne. The journey lasts for about a 40 days.
By Plane : count at least 700 euros the trip (about 20 hours of flying). Chose your airline with attention, because on such a long trip, you will need a minimum convenience . Asiana Airlines has a really good value for money.
By bike : count several billion of pedal turns and a journey which should last more than a year. Unbeatable value for money.