Cost of transporting tomatoes

Roughly what percentage of the price of a tomato comes from the cost of transporting it in a truck?

The following incorrect solution illustrates one of the main ways you can go wrong in order-of-magnitude estimates.
Incorrect solution: Let's say the trucker needs to make a $400 profit on the trip. Taking into account her benefits, the cost of gas, and maintenance and payments on the truck, let's say the total cost is more like $2000. I'd guess about 5000 tomatoes would fit in the back of the truck, so the extra cost per tomato is 40 cents. That means the cost of transporting one tomato is comparable to the cost of the tomato itself. Transportation really adds a lot to the cost of produce, I guess.

The problem is that the human brain is not very good at estimating area or volume, so it turns out the estimate of 5000 tomatoes fitting in the truck is way off. That's why people have a hard time at those contests where you are supposed to estimate the number of jellybeans in a big jar. Another example is that most people think their families use about 10 gallons of water per day, but in reality the average is about 300 gallons per day. When estimating area or volume, you are much better off estimating linear dimensions, and computing volume from the linear dimensions. Here's a better solution:

Better solution: As in the previous solution, say the cost of the trip is $2000. The dimensions of the bin are probably 4 m × 2 m × 1 m, for a volume of 8 m³. Since the whole thing is just an order of magnitude estimate, let's round that off to the nearest power of ten, 10 m³. The shape of a tomato is complicated, and I don't know any formula for the volume of a tomato shape, but since this is just an estimate, let's pretend that a tomato is a cube, 0.05 m × 0.05 × 0.05, for a volume of 1.25 × 10^-4 m³. Since this is just a rough estimate, let's round that to 10^-4m³. We can find the total number of tomatoes by dividing the volume of the bin by the volume of one tomato: 10 m³/10^-4 m³ = 10⁵ tomatoes. The transportation cost per tomato is $2000/10⁵ tomatoes=$0.02/tomato. That means that transportation really doesn't contribute very much to the cost of a tomato.