My 2BHK upgrade to M3M: Gurugram's real costs

Gurugram mein 3BHK ka real all-in cost quoted price se bohot zyada hota hai. I'm upgrading from my 2BHK, looking at M3M in Sector 88A. Builder se kitna negotiation expect karoon? 5-7% milta hai kya? Hidden charges, possession ke time kya kya extra lagta hai besides stamp duty? Advice do.