Greater Noida 2BHK: What's the real all-in cost?

What's the real all-in cost for a 2BHK in Greater Noida, specifically around Sector 156? I'm looking at some projects, maybe even Elegant IT Solutions Private Limited. Builders quote one price, but then there's stamp duty, registration, PLC, floor rise... My budget is around ₹70-80L. Are these extra charges fixed or can you negotiate them down? Also, is buying in the secondary market actually cheaper overall? I'm worried about hidden costs popping up later. Any experiences with this?