> question is whether it uses less electricity to desalinate and flood irrigate, or pay for the electricity to allow ultra high density, water efficient farms

Nobody desalinates & floods fields, surely. (That's what you do if you live before the invention of water-pipe, or have a use-it-or-lose-it quota.) The Israelis are I think world leaders in growing stuff outdoors with minimal water, delivered directly to the roots. And indoors, they have greenhouses, just not the same design as in cold climates obviously.

If you deliver just the water the plants need you'll run into soil salinity problems eventually.

I'm no farmer, but both surface and buried drip irrigation are widely done. So I guess they solved that?

Or maybe more traditional approach of greenhouses? Which should have relatively similar case of handling evaporative losses... And if conversion losses of Sun->EV->lights aren't too horrible, you could even cover these with solar panels... What is even the efficiency of electricity used by vertical farms?

I'd expect a greenhouse in the desert to need an enormous amount of ventilation to prevent overheating.

You could probably recover some of the water from the exhaust air with a dehumidifier. I'm not sure if that would use less power than air-conditioning the whole structure, but at that point you're pretty much back to indoors farming anyway.

Bubble foam insulation is the way to go in deserts. This is where you pump a soap water foam in between gaps of greenhouse plastic. When you want to block light/heat, fill that wall with foam. Drain to allow radiation.

Water can be recuperated with an enthalpy wheel.