The cost advantage of using thorium will depend on the type of reactor you're using and how the regulatory commissions plan to deal with it. Generally thorium provides the immediate advantage of being accessible anywhere in the world even if you don't have concentrated deposits (terrestrial rock like granite contains 8-13 grams of thorium per tonne). Thorium is also dirt cheap rather than being a special grade of fuel that can only be produced by nations with centrifuge technology, like enriched uranium. So you should save some money with thorium reactors over enriched uranium reactors, but that's negligible compared to regulatory costs anyways.
India's heavy water thorium reactors should be hit with similar safety regulations as any other water-cooled reactor depending on the country. The costs from regulations are arguably the biggest capital bottleneck to building new reactors today, even safer ones. Over 75% of nuclear costs in the US are attributed to regulatory processes rather than the actual material and technical costs of the reactors themselves.
http://www.phyast.pitt.edu/~blc/book/chapter9.htmlIn India and China however, you'll find nuclear reactors cheaper to build and decommission than coal plants, simply because their regulations are more cost and time efficient while still being very severe.
Nuclear will also be required if one ever hopes to go fossil-fuel free in the future, as it is the only clean source of energy apart from hydroelectric dams that can supply reliable enough energy to cover baseload energy needs. Solar and wind simply cannot compete with coal in terms of cost-effective reliability because they are too intermittent.
