TIL at some point in the last 80 years, the cost of a blowjob from a Chicago prostitute went from being more expensive to less expensive than vaginal sex, as the societal taboo against oral sex – which gave it scarcity value – declined. (The average price of each is currently $37.26 versus $80.05.)

http://www.theguardian.com/books/2009/oct/12/freakonomics-global-warming-statistics