India's Tata Motors Ltd unveiled the world's cheapest new car on Thursday, bringing car ownership closer for millions of poorer consumers in emerging markets but raising enviromental concerns.The 4-seater Nano, with an engine around 625cc, will have a dealer price of 100,000 rupees ($2,500), about half the cost of the cheapest car on today's market, a 25-year old model from Maruti Suzuki Ltd, Tata's great rival.