Does negotiation really work with Goyal Builders?

Does negotiation actually work for a 3BHK in Meenakshi Garden with Goyal Builders? I'm upgrading from a 2BHK in Dwarka, and they quoted ₹3 Cr. Agent bol raha hardly any room. But what's the real all-in cost? Stamp duty, PLC, parking fees - kitna extra lagta hai? Aur possession pe hidden charges ka kya scene hai?