Pricing between two similar products doesn't necessarily reflect difference in impact on the environment. It can also indicate scarcity in resources, an advantage in being the first (which may include setting your own price), protection by patent, or monopoly. Also, scale is another variable. While a rural area may have less-expensive housing and transportation costs than a major city, the city may have more efficient delivery methods and transportation (which could include the upkeep of having lit and paved roads to encourage walking), when accounted for on a per-person basis. However, with some refinement, I think your theory could be potent.

The economy of scale is a good point. I'm not sure there is necessarily a linear relationship between cost and energy use. It is more likely super linear.

In my mind, the costs passed onto the consumer in terms of pollution seem to be a big hole in the theory, though I do like it. Is there some way to theoretically cap it? Otherwise, it isn't possible to even hypothetically say how much price correlates with environmental impact.