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?
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.
This. Assuming you don't splurge on cigarettes or other money wasting stuff, you could do reasonably well here at Malaysia, Thailand, The Philippines and probably Singapore. Note that $900 a month at Malaysia is the average wage of a fresh graduate with 3-4 years of experience. You probably couldn't get a house/apartment at the major cities though.