The cost of transporting the conventionally grown plants would have to be accounted for as well, but I'd be pretty surprised if that got anywhere near tipping the scale over to vertical farming.
I wonder if that could be solved more easily. Build sufficient rail network and hydrogen/electric/other zero-carbon trucks to move produce from production to there and then train it in. And this is really a sector we could fully automated almost already.
Switch hydrogen for methane and produce that methane in a bioreactor from the food scraps. These technologies are already here, no need to wait for a future hydrogen car.
Also, building a zero-carbon transport system would be generally useful for transporting things other lettuce. And that's probably like 80% of the way toward a zero-carbon transit system. I think you have a good point.