The detailed fee structure of IIT Bombay is as follows

Unless you study in an IIT, you will never understand how much the Government invests in an IITian. The semester fees along with hostel fees are more than 20-30k. 

The students who got admission through GATE, receive a monthly stipend of around 15k which compensates for the meager fees spent. You can spend the rest of the money on your expenses. Moreover, all the essential commodities are made available on campus that too at reasonable rates. So one can even say that you are studying free of cost with money from the tax-paying public.