It's been awhile since I was on teh Aerolineas Argentinas website, but it's good to see they have revamped the site. You can also now pay online with a US Visa card (if you log in via the US site), instead of having to do it over the phone. finally!
@amat .. if you will book your trip through www.expedia.com you will get the same price you found on Aerolines "Argentina" website and can pay with each MC/Visa/AmEx online I use this way for long time.