Confused about 3BHK upgrade true cost

Budget finalised, loan pre-approved — now stuck on which sector. Currently in a 2BHK in Dwarka, thinking of upgrading to a 3BHK in Vasant Kunj or maybe looking at Green Valley Builders projects. My budget's around ₹3.5 Cr. I'm trying to figure out the *true* all-in cost for a 3BHK. Beyond the base price and stamp duty, what are the hidden charges one should really watch for? Builders always mention PLC, parking, but what else pops up unexpectedly? Also, is going for pre-launch pricing actually better in Delhi? Or do they just inflate the initial price to show a 'discount' later? Is the price jump from my current 2BHK worth it for these premium areas? Already have a home loan, so need to be super smart.