Sorry for the late post, but hopefully this can help someone with the same question.
I just traveled through Central and South America and found both Hi-8 and MiniDV (which is what I used) in all big cities. Hi-8 is a lot more common but I bought MiniDVs in Guatemala, Ecuador and Argentina without any problems. I do suggest that you do not buy any of the products without plastic wrap, which can be commonly found.
I never paid less than 7 dollars and never more than 9 for each tape, which is comperable to US prices.
Also, I did have some problems with the tapes I bought in Ecuador, but the lack of tape quality could have been more due to the pounding my video camera took in the Salar de Uyuni. Not sure.
Finally, Mini DV is much better than Hi8 for doing presentations and manipulation of the images.
For a sample video (highly reduced for quick loading time) check out some of my trip video from South America on my website.
flash plug in needed