There is big demand for English in Kolkata,one of the major cities in India.There are a lot of students who go for studies abroad and many who migrate to other countries,There are only two or three institutes which have foreign teachers teaching languages.The demand for french,German,Spanish and Italian is also in great demand.the idea of running a course for TEFL,TESOL is great since there arent any such institutes doing so.Kolkata is the cheapest city in Kolkata .you can start of with an initial investment of USD20,000-40,000..You will have to come to India to get a clear view of the things I hav been talking about.You can have a lot of volunteers who could teach in your school in return for food and safe accomodation.
Do get back to me if you need any further clarifications.