Greater Noida builders hide costs until the very end

My lease ends in 4 months and I'm stressed about hidden charges for a 3BHK upgrade. I'm currently in a 2BHK near Sector 137, eyeing Lavish Buildmart in Sector 140A. The quoted price seems decent, but I hear about crazy charges popping up at possession – like unexpected power backup or IFMS. Is this still a huge issue in Greater Noida? How much extra did you actually pay over the initial agreement? What should I watch out for?