Sagy - good suggestion, I didn't realize it was that much cheaper for NZ. However, at this point I don't think that will work for us. We are definitely starting in SA (I am heading there next week for Spanish lessons!) and we don't have any more miles to get over to NZ. Plus we like the Eastward itinerary.

christep - Yep, I think you're right. I tried starting at some other SA countries and they all have varying amounts for the taxes. In the end I think we'll stick with Ecuador because once we buy flights to get to the new starting country the savings are a wash (we have to physically start in Ecuador due to other plans). But for anyone interested, here's the tax amounts I found in other countries, using the online tool:

Country, Sales Tax %, Sales Tax $USD for LONE5
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Ecuador, 12%, $468
Argentina, ~5.5%, $210*
Peru, 19%, $741
Brazil, <1%, $36
Chile, 0, $0
Colombia, 8%, $312

* When starting Argentina there was also a huge fuel surcharge, $300