I don't know about reward tickets in Peru, but I do know for cash one-way you are much better off buying a return ticket and not taking the return trip. (Between Buenos Aires and Lima the travel agent had quoted me $700 one-way but I looked harder and found myself a return flight for $300).
Easter Island is totally doable as you can now fly LAN from Lima direct for about $300 if you book early enough - I have my flight booked for Easter Sunday (by accident) and I will let you know how that goes!