What is the cheapest car in the world?

One possibility is the Tata Nano (4-passenger city car), which had a 2009 base price of 142,000 to 195,000 INR ($2800-$3900 USD).

The Tata Pixel concept car, first introduced in 2011, had a lower base, at 120,000 INR ($2500 USD). It was scheduled for marketing in mid-2012.
Tata Nano-Price:$2500
You can buy a few cars that are pretty good price. You can go for a compacted car that is small and good on gas.