One more plusgrade upgrade. My premium economy GOI -> DEL ticket was purchased on 4/30 for Rs 8,097. The business 'value' ticket price was Rs 30,474 at the time.
I received a plusgrade upgrade offer of Rs 11,894 today, for a total price of Rs 19,991. The business cabin showed 5 of 12 seats taken when I did a seat selection (my upgrade was the 6th).

I wonder if these plusgrade prices change? Would the price be lower/higher if I wait until just before the flight?