Greater Noida negotiation: What they don't tell you

Sector 150 keeps coming up every time I shortlist something. I'm finally fed up of renting, landlord hiked rent again, so taking the plunge for a 2BHK. Looking at GSB Townships' projects there. My budget's around ₹75L. Does price negotiation actually work in Greater Noida? Sales reps act like prices are fixed. How much can you realistically knock off the base price? Or is it all just adjusted with PLC and other charges later? I don't want to get surprised by huge extra costs at possession. Any real-world advice on negotiating the final deal?