I flew my bike from Cologne/germany to Buenos aires lasr december. It cost 3 Euro per Kilo, my Transalp (Frontire, Mirror, Windshield, boxes detached) cost 800 Euro. The first question of the customs in Buenos Aires Airport was Carnet de Passages Por Favor. Other biker we met had the same experience.
But the airport is otherwise recommendable, it was fast, friendly and efficient. We paid 70$ handling fees per bike, nothing else. But be careful, the charge hefty parking fees, if you do not pick up the bike within 24 hours after arrival.