We are in Expiry week, so during this period Long ITM Options need additional margin as per exchange requirement.

The Exchange charges physical delivery margins as a percentage of applicable margins (VaR + ELM + Adhoc) of the underlying stock which is levied from expiry minus 4 days for long ITM options.

What is the usual value of (Var + ELM + Adhoc) for a contract of SBIN 300 CE?

[Assuming that stock is trading just above 300 and lot size is 3000, contract value is 900000 Rs.]
The post mentions that the margin keeps increasing from Friday prior to expiry week till the expiry date [10%, 25%, 45%, 70%].

You can check the VAR, ELM and ADHOC margins on NSE website. Refer to this page for SBI stock.

SBI’s VAR + ELM + ADHOC margin is 21.6%. So for contract value of 900,000 the applicable margin will be 194,580. On expiry minus 4 days you’ll need 10% of this margin if your Long Option position becomes ITM, so on and so fourth for other days.