The standard smallcase charges would apply to NRIs as well.
That is, Rs. 100 + GST (18% on Rs.100) or 2.5% of the investment + GST (18% on fees), 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