I should correct myself. It's weight, not volume. The issue is that if there are alternative ways to transport things that are not perishable—i.e., by rail, by car, by truck, sealift, or whatever—then there are ways in which you can reduce costs overall by stocking up and thinking ahead. It doesn't necessarily mean that things will cost more.
The things that cost the most are the perishable nutritious foods like milk and eggs, which you can't stock up on using other transportation methods.