Just because you don't see it in the price tag doesn't mean you're not paying

One concept in economics is the notion of opportunity cost - from Dictionary.com, the cost of an alternative that must be forgone in order to pursue a certain action. Put another way, the benefits you could have received by taking an alternative action.

This leads us to accounting profit vs economic profit. You start a business, and it's your first year, and you've managed to keep costs down while gaining market share. You break even - zero accounting profit. But you have made an economic loss, because you could have been at your old job, making money. And you gave up that opportunity to start a business.

Hopefully, your business does well. But this example highlights the fact that some costs don't come in the price tag or on the financial statement. This article on MSN Money tells us how to go green on a budget, but it also has a little blurb about how the true costs of conventional food may not all be in the sticker price:

Some economists argue the true costs of conventional food are not reflected in the price consumers pay. The negative effects of conventional agricultural production on water, soil, air, wildlife and humans total $5.7 billion to $16.9 billion a year, economists Erin M. Tegtmeier and Michael D. Duffy of Iowa State University concluded in a 2004 study published in the International Journal of Agricultural Sustainability. The study shows "consumers pay for food well beyond the grocery store checkout" in higher utility bills, taxes and in declining environmental and personal health.

Such "hidden" costs are part of the reason why advocates for green buying practices argue consumers need to rethink their consumption patterns and focus less on the cost of individual items.