We are leaving in January for 3 months with our van , as an idea of costs , trip across is costing us $1214.00 for 2 adults , 1 twin bed Porthole , 2 x passengers private cabin ( Night Trip Across ) for a total length of car and van of 13.3 m . Return trip is $952.00 with 2 Recliner Chairs booked ( Day return Trip ) . We are hoping that 3 months will be enough . Also purchased a National Parks Pass for 12 months at a cost of $ 36.55 with seniors Discount .