Define "live on". Are we assuming living somewhere permanently or living there temporarily (like the whole back-packing through Asia thing)? Are we talking about people who are debt-free? Talking about staying in hotels/hostels or renting a home? Running a car or using other means of transport? Including the cost of getting there or not? What - specifically - do you intend that $30 per day covering?
You have nothing but what you are wearing and a voucher for a one way trip to anywhere on the planet.
You magically gain the equivalent of $30 USD worth of purchasing power once per day, wherever you end up.
Where do you go?
SE Asia (including Indonesia). Some of the Pacific Islands also have a low cost of living if you're living like a local but are expensive if you're living there as a tourist. You could live extremely well in Tonga for $30 per day if you leased a property rather than back-packing.
I'm not familiar with South America myself, but I believe there are parts of South America where you can live very well for very little (by Western standards) as well.