Rs. 20/- non judicial stamp is enough.
You may purchase stamp paper at coimbatore, it is valid.
but your risk it. you may purchase it thane, for awoid of language (tamil) promblem, you face at notary office, becoz thane notary not known tamil.
but in stamp paper, your name and village and stamp vendor name and address mentioned in tamil.
so you purchase at thane, by 94432838171