It is not that simple. Back in the 80's & 90's I was part of a group that did extensive studies on renovating Central and Egmore stations in Chennai.I'm only familiar with these two stations. Our report had to deal with the fact that both were Heritage buildings and had to stay 100% operational at all times. We estimated a 15 year timeline for complete renovation, including new parking, sewer system, renovation of drainage canals, new circulation, multiple new entrances, expansion to 3 times present sizes, modern concourse equipment, complete demolition of existing platforms, equipment to handle uncontrolled toilet discharge, repair of existing structure, earthquake retrofits, replace corroded cast iron members,etc. I could go on and on. Just parking, new entrances & circulation, both underground and overground, was a 10 year project. We estimated Chennai central had a need for 8,000 parking spaces by 2020 against about 1,200 available. There were 3 underground parking levels and 2 new underground levels to Central itself. Arrival and departure access was in two separate levels similar to Airport.
Our cost estimate way back then was in the Rs 4,000 crore range for both. More like Rs 15,000 crore right now. Or the entire cost of Chennai metro Phase 1. People don't appreciate the scale of the Central complex or the monumental costs and effort needed for such an effort. We had to renovate roughly 230 acres of land. Also there is no hope of paying for this through toilet ticketing and advertisements. It is a question of cash priority.
Our recommendation also was not to do anything cheap and half-a$$ed. Wait till you have the time and money to do a proper renovation. Till then some cosmetic improvements can be done.
My best estimate comparison would be the Renovation of St. Pancras station in London. This was not a complete renovation. For instance the concourse and the railway traffic was not reworked. The station was also completely shut down during renovation. Traffic is roughly 1/12th that at Chennai Central. Still the final cost was roughly $1.3 Billion estimated in 1995. Probably about 2.5 Billion now or about Rs12,000 crore. Work started in 1992 and final pieces were finished in 1999. World class is not cheap.
That Rs 12,000 Crore could pay for an entire Phase 2 of Metro adding about 60-80 km of overhead lines.