Regarding packing: My wife and I each carried a 40L backpack. This is pretty small, but I'd highly recommend it for this kind of trip. They were a godsend on buses in South America.
Cost: Over the course of the trip we spent almost 40k ($165/day), if you exclude Antarctica it was a much more reasonable $92/day. Last minute deals for Antarctica DO exist, I recommend them highly (we saved somewhere in the neighborhood of 20k).
Transport: As with others in the thread, we bought as we went and opted primarily for overland travel. Tips for 30 hour bus rides: carrots to snack on and Harry Potter audio books.
My most recent post [1] was a wrap up after being home for some time. You can check out the blog for more on packing, budget, etc.
Happy to answer any questions.