EUR 1800 is about as low as you will find. On Oneworld you can get to PPT from SCL on LA, so you have to have xONE5 ticket if you want to visit both Australia and PPT. Otherwise NZ (STAR) flies to most of the south pacific. Not cheaper using RTW ticket but with more travel and maybe flexibility. There are no good solutions for what you want to do (that I've found in the past).