As a secondary SIM, BSNL would be the best bet. Taking a secondary SIM of Jio would entail a monthly recharge of ₹155 to keep it active. You could recharge yearly, but even then you wouldn't save a lot doing so.
Surprised to say this but among the private operators, Airtel offers the lowest denomination plan with paid outgoing SMS at ₹99 /28 days. Vi comes second with a variety of plans ranging from 28 days to 31 days, but all of them starting from >₹120. Jio's plans are the most expensive @₹155/ 28 days.