I think the issue here bigal is that Adani needs the coal for...

I think the issue here bigal is that Adani needs the coal for its in-house domestic use in India - so the price per ton is not a deterrent in this case.  They need the coal! Here's an extract from their web site

• More than 90 percent of coal in India is produced by the government-owned companies. CIL is one of the largest coal producing companies in the world.
• The role played by private sector players is limited to captive mining for the purpose of self consumption, be it steel production, power generation, cement production, fertiliser production.
• Currently, in spite of large reserves of coal, the industry is unable to increase the coal production to match the demand and to reach its potential production. Hence, India has to import coal to meet its additional requirements.
• Indian power sector relies heavily (around 78 per cent) on coal for electricity generation. As the infrastructure to support coal imports is inadequate and coal reserves are found in abundance in India, the domestic coal production has to gear up to meet future demand.