LAN Chile also has an airpass; if flying into South America on LAN:
http://www.latinamerica.co.uk/visitsa01.htm
$308 one way to Easter Island

If flying another airline it is $433 (not worth it)

I'm seeing $819 on Travelocity for some dates in July; this is about what I paid when I went in 1998. I've seen occasional sales around the $600 mark, but that is pretty rare.

I'm seeing a $574 price from Buenos Aires on Travelocity, but no available dates.

Despegar.com also sometimes has specials.