A head of organic lettuce retails for $3.54. Ref link.
Let's say all things being equal someone can pick 300 heads per hour. Let's say you pay them minimum wage of $8.00/hr. So per head picking costs: 8/300 = 3 cents/head. But you can't get anyone to do it for $8.00/hr. So you import Mexicans and all the social problems that go with it. But maybe you could get locals to pick for double min wage, say $16.00 hour. Now the per head labor costs SKYROCKET to a whopping 6 cents per head. The retail price SHOOT UPS fro $3.54 to $3.57 per head! OMG! the world is ending. Import more Mexicans I paid 3 cents more per head!!!!
I buy regular red leaf lettuce for $1.38/head. This lasts about a week-10 days for 2 people. Iceberg fluctuates more and is recently $1.68/head. It lasts longer. we use it for sandwiches. And I use Green Bags to prolong produce life.
I don’t know the pay scale for vegetable picking. I remember when lettuce was 1/2 the price it is today. Sometimes I grow my own.
From what people tell me, the pay is not what keeps Americans from doing the work. It is the nature of the work: repetitive, sweaty and boring. American workers want more autonomy.