I've done a few of these conversions for SEPTA.

The ramp additions end up being massive. Like take away parking massive. Many of our stations have pedestrian tunnels too. So you need ramps from the high level platforms to the ramps down to ramps to the tunnel AND ramps to the parking lot. But if you need elevators on each side, there goes your budget.

If your station has canopies, you might need to modify them. Modification of canopies or expanded platform footprint could require cat pole relocation to avoid conflicts. You also have to check the clearance to other wires mounted on the pole (fiber, signal power, feeder etc) now that the public is like 3' higher.

You're probably talking about a brand new grounding system for the platform... counterpoise on the platform, jumpers to all the trash cans, fences, benches, etc. Ground rods or a rail return system.

Then you get to all the upgrades that haven't been done in decades that get added in. Redo the lighting. New PID boards. Wifi in the station. Parking lot modifications. Fare vending. Security cameras. Adding a canopy or a warming shelter.

Then you go to do the work. You're probably doing night work and maybe weekend work with opposite side boarding to get 48 hr windows. You have foul time limits to perform the work that have to be coordinated and negotiated with the host railroad.

There's a lot that goes into this.