My book is mostly about two prices--something and nothing--but at dinner in NYC with Jay Walker this week, he convinced me to include a discussion of a third price: less than nothing. That's right, a negative price: you get paid to use a product or service, rather than the other way around.
This is more common that you might think. Online, you see this in things like Microsoft paying you to use their search, but it actually has a long tradition in traditional marketing. You find it instant rebates and cash back marketing, and in the cash rewards, frequent flyer miles and other payments you get for using credit or loyalty cards.
Jay pointed out that a cashback rebate invokes a very different psychology than simply saving the money in the first place. For instance, he says that studies of how people spend the $1,000 (or whatever amount) check they get when they buy a new truck (or, more to the point, finance it), show that they tend to spend it like a lottery winning--an unexpected windfall. Guys would buy golf clubs that their wife would never normally let them purchase, and their wives wouldn't stand in their way. This despite the fact, which they must know, that they'll be paying that money back over the years to come, just like a credit card debt.