Most PhD students (and by most, I mean an overwhelming majority of them), receive scholarships, grants, financial aid, and also get Teaching Assistantship opportunities, which pay for their fees.
The opportunities get better, if you go to better places, and you'll go to better places if you do well during your BS-MS degree at IISER.
So work hard, and you'll surely succeed.
Anshuman Acharya, former Visiting Master's Student at Harvard-Smithsonian Center for Astrophysics (2020-2021)
Source: Quora Digest