Chennai Mathematical Institute

Hello Satyam,
For M.Sc mathematics, the tuition fee is Rs1, 00,000/- per semester (two semesters in a year).
For MSc Mathematics, a substantial number of scholarships will be available, consisting of a full waiver of the tuition fees. The number of scholarships will be roughly equal to the number of students admitted in recent batches of M.Sc maths.
Feel free for your further doubts.
Good luck.

https://www.shiksha.com/university/chennai-mathematical-institute/exams/cmi-entrance-exam.

If you have good score in academics then I think you don't have to drop a year, you will get admission in that directly.

Please refer to the link below:
https://www.shiksha.com/university/Chennai-mathematical-institute/exams/cmi-entrance-exam/syllabus.

To apply for Ph.D. in maths you must have an M.Sc. Degree in Mathematics or equivalent and students with a Bachelors degree in Engineering or Science with a strong aptitude for research. Please refer to the link for further information: http://www.cmi.ac.in/admissions/.