Just another point.
I flew from BA to ushuaia for around 50 quid. takes 3.5 hours compared to 3.5 days on the bus!
They took all my stuff and bike for no extra charge despite the 15kg weight limit!!!
You can't book online, you have to go to the main office in BA and buy your ticket in person. Bit of a faff. It was fairly easy option for me as my bike was still in it's box.
Also I have heard people doing a 2 week spanish course in BA and getting a "student residency" paper which, when you book your flight, gives you half price tickets. Bit dodgy that though...