The same way any new tech goes down in price - commoditization, automation and economies of scale.
It's unlikely they'll feed a million people all the food they'll need but it's likely they could feed a million people all of the leafy greens they need.
"commoditization, automation and economies of scale."
Traditional farms have the clear and overwhelming advantage in all three of these. And they aren't standing still either, they benefit from the advance of technology too.
The major advantage this has is that it shrinks the supply chain. Transporting fresh leafy greens is a bit of a nightmare because they go bad so quickly.
I don't expect these things to compete with a farm growing potatoes for a long while or even anything which keeps well enough in a fridge.
It's unlikely they'll feed a million people all the food they'll need but it's likely they could feed a million people all of the leafy greens they need.