Tough question. Airfare, for any FlyerTalker, would be free.

I'm flying SFO-SCL on AS miles and the tour company gets me to USH as part of the package.
My guess would be that $8Kpp for the cruise would be the least you could get by for, though I have no operator in mind who might do that.
Lindblad, for example, currently offers a rate of $10,250pp from SCL, but that excludes tips and whatever else you might by while enroute.
But a;lo be careful. Regent Seven Seas costs more and it a much larger ship, offering much less time on land.