Sohna 3BHK upgrade: true all-in cost kya hai?

Budget finalised for a 3BHK in Sohna, but I'm stuck on understanding the true all-in cost. Currently in a 2BHK in Sector 65. Builders like M3M or Godrej quote super area, but carpet area mein kitna difference aata hai? Hidden charges jaise PLC, parking... are they really worth it? Construction-linked plan better hai?