Hidden charges drain New Delhi ROI

₹75,000 every month for rent for 3 years, almost ₹27L gone. Finally taking the plunge. I'm eyeing a 3BHK in Gulmohar Park, Kohli Builders ka project hai. Quoting ₹2.1 Cr. My big question: negotiation pe kitna expect kar sakte hain? Builders bahut firm rehte hain. Also, what are those hidden charges at possession? Like maintenance corpus ya electricity connection fees, jo baad mein surprise ban jaate hain. Koi tip hai inko pehle se uncover karne ki?