What is the minimum recharge amount to keep alive Airtel,Jio,Vi and BSNL incoming calling services?

I have 2 Idea Prepaid numbers. I just recharge Talktime of Rs 100 for which I get around Rs 84 or 85. Idea automatically deducts Rs 46 to increase validity by 28 days. Earlier this amount was less (I guess Rs 35), but now they are increasing this amount. I think Airtel almost deducts similar amount to keep number active for 28 days.
But if balance is below Rs 46, then Outgoing stops and I get message that Incoming would also stop after few days. But so far I have never been in situation where incoming was also stopped.
I think this is still better as all Operators are having Postpaid plans of 200+ amount, so unless that is your primary number which gives good call quality and good internet, there is no point is paying that much.
Cheapest is Rs.48 with 3GB data
or Rs.49 with some talktime + 100mb data
There is one Rs.29 plan with 2+days validity and 200mb data n unlimited calls.
Don't go for talktime plans , not easy to track balance left n deductions.