You're only counting the build cost though, they cost anywhere from $1-2 billion a year to operate depending on which article you read. Considering an aircraft carrier's service life is usually around 40 years, that's quite a savings just from removing a single carrier group from the fleet. That would pay for anywhere from 50-80% of your estimate right there. I'm not discounting the 40-50 years of rail maintenance, but you would hope rail service could at least come close to breaking even by selling tickets. There's no profit coming out of an aircraft carrier group, unless you're the one selling them the supplies.