You may have arrived at this page via a search engine - certainly you used a computer to get here. We often think of these things as being free - computers are like phones, they are just there; search engines don't require me to input my credit card information before I can see the search results. However, if you look a little closer things start to seem different.
Let's start with the computer - we are all vaguely aware that it is costing us money. Firstly, we had to buy the machine. Secondly, we have to pay for internet service. Most importantly, however, we have to pay for the electricity to run it. But how much does that cost? Eric Shufro, who writes at OverClockers.com, has an interesting article that address just that question: How much does it cost to run your PC? His scenario is for 24 hour up time (not your typical use) and comes out at around $50 per month. So per hour, this is about $0.07.
So how about the search engine? It is interesting to look at two sides of the equation here. Firstly, let's take Google. In 2007, it cost $11B (yes, 11 billion dollars) to run Google. This is the total costs and expenses line item from their 10-K filing with the SEC. Google served about 7 billion searches in December 2007. If we assume all of 2007 was the same (which, of course it wasn't) then that would give us 82 billion searches coming to 13 cents per search.
Ok - so that describes the cost to Google of providing a single search, but what does it cost you? One way to look at this is to consider what funds Google. As Chris Anderson points out in this interview, one can consider advertising budget as the cost to the consumer of an ad supported model. Chris makes the point (in reverse) about Craig's list, suggesting that the money that this service has taken away from classified ads in news papers makes everything a little bit cheaper. This is similar to the comment I made in an earlier post about the concept of 'free'. To summarize: 2007's internet advertising is estimated to be around $20 Billion. That amounts to more than $50 per capita for the US (in other words, over the course of the year, $50 of what you pay for stuff is used to attempt to persuade others to buy it as well).
As I get time, I'm hope to cover some other examples like this, as well as drill down on the ethics of the idea of invisible costs as well as externalities.