Upgrading to 3BHK: Price jump & hidden costs confusion

Currently in a 2BHK in Sector 137, thinking of upgrading to a 3BHK or a small villa, but the price jump is confusing. I'm looking at places in J Block, maybe Intellicity, budget around ₹1.5 Cr. Builders ka negotiation kitna realistic hota hai? Like, 5-10% off the quoted price possible hai kya? Aur possession ke time jo hidden charges aate hain, unka kya scene hai? Stamp duty, registration ke alawa aur kya expect karu? EMI already chal rahi hai, toh total cost of acquisition sahi se calculate karna hai. Koi real experiences share kar sakta hai?