AFAIK (my data is from February 2015) paid entrance to the ITC Green lounge is about ₹900 or 1600 depending on what package you pick. The PP next door has a similar price. Curry kitchen beside the lounge complex offers you a combo of a curry and a soda for ₹330, and little further on the nice bar with view of the tarmac (which sadly none of the lounges in DEL have) will serve you a beer and a snack for less than ₹600-1000.

I occasionally have 3-4h layovers in DEL T3 at night and have tried out all the lounges with the exception of the EK lounge. All of them are pretty full at night, the ones in B (SQ, LH, PP) are rather dark, the ones in A (AI, ITC, PP) are more of an exclusive waiting area. I especially dislike the openess of the ITC and PP lounge where everyone can look in.