The lettuce is grown in my own country and is already picked and tended to by low-key slave labour (migrant workers).
It’s mostly in the time value, but the ratio of value to weight/volume is also much lower (which is going to result in logistics affecting the price a lot more). The biggest factor is that the clock is ticking for the lettuce going bad, and also that it needs to be refrigerated at every step along the way. Logistics are expensive! It’s the difference between night and day when time/refrigeration doesn’t matter.
The logistics involved in getting a TV to a grocery store is nothing in comparison. There’s no risk factor for delays (this risk is incorporated into the price of lettuce) and the total time between manufacture and floor-display doesn’t matter.
I meant steel beams as an example of logistics with special constraints. In the case of steel beams it’s extreme total weight/size/shape.