Well, the expensive flights are the ones to the South Pole itself. If you just wanted to get to Antarctica and snowshoe/ski around, the fares start at $16,950. Of course, this includes accomodations, activities, food, etc.. while you're in Antarctica. So, it's more like a week-long tour.

I imagine that if you wanted to do a private expedition of some sorts where they simply fly you in and dump you in the middle of nowhere, that the prices would be a bit lower.