The standard smallcase charges would apply to NRIs as well 

That is, Rs. 100 or 2.5% of the investment (whichever is lesser), per smallcase that you buy 

Please note that the Zerodha charges that are applicable, are separate. The charges for those with an NRI demat account are 0.1% of the investment or Rs. 200 (whichever is lesser) per executed order. More details on other applicable charges here

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